idle issues and sudden bucks!! please help

[revhead347]

You shouldn't have to mess with the idle screw at all. Like I said, the IAC is known to have problems. Cleaning the IAC out with carb cleaner doesn't do squat. That just removes the dried up oil and gunk out of there; the problem lies in the electronic part, not the valve. You can buy one at an auto parts store for under $100. I was an assitant manager at an Advance Auto Parts, and we used to sell them for $84. We had a no hassle refund policy, which I assume just about everyone has. If it doesn't fix your problem, you can return it. I wouldn't suggest changine a whole list of things like you mentioned, that is just a waste of money. You will never get better parts than what came with your car, so changing something that isn't broken could just set you up for a failure. The MAF hardly ever fails, so I wouldn't change it. The TPS can fail because it has mechanical moving parts in it that wear out. You should also check the TPS like stng94 said. You have to have a digital voltage gauge. Factory spec voltage is .98 volts at idle. I've found up to 1.02 volts to be acceptable. Just hook the positive side to the green wire coming out of the TPS, and the negative to a ground.

Kurt

 

[96darkhorse]

It might be. If you experience sudden bucking when you are driving it's a dead give away of an IAC failure.

Kurt

this is exactly what i go through besides the weird idle; once in a while i get a high idle, but thats very few times.i tried cleaning the iac but no thing happen....i guess ill try to replace that...i can get it new for like 40 bucks

 

[Silver85TC]

"He said the idle speed problem was exactly the same no matter if the car was hot or cold. That rules the ECT out. A bad ECT would make the car run richer than hell, and trigger a CEL."

Absolutely WRONG,WRONG,WRONG!!! A bad ECT could cause the car to run rich OR lean. Also,it may not trigger a CEL.

The ECT sensor can be way off and not trigger a CEL. How you ask? These sensor's are notorious for becoming extremely lazy with age. They then tend to react to different temperatures VERY slowly. Why don't they trigger a CEL you ask? Because a CEL is only triggered when the output from the sensor is outside the programmed parameters stored in the computer and that range is VERY large.

So how does this affect your idle? For example, say your sensor was sending an output 25 degrees warmer than what the actual engine temp was(your comp has no other way of knowing how hot the engine is.....that's what the ECT is for!). This would cause your air/fuel ratio to be way off. (your comp adds the appropriate amount of fuel based on the engine/air temp on a cold engine). If the temp the sensor was sending was warmer than the ACTUAL engine temp, the comp wouldn't be adding enough fuel, therefore creating a lean condition which can present as bucking.

I should also mention that I had this exact problem in the above example. I only figured it out after measuring the actual output from the ECT sensor. The resistance was way off for colder temps, but was almost spec at normal operating temps. I should also mention that the faulty sensor was a 3 month old NAPA part. I had an old Ford ECT sensor from a different car lying around. Checked it with a DMM and found it was still in spec. Installed it and my cold idle/bucking problem were fixed. An IAT sensor can cause idle/pinging problems as well.

For more Ford ECU info check;
http://fordfuelinjection.com/index.htm

So, I say ONCE AGAIN, if you're IAT/ECT sensors are old, REPLACE THEM with new Ford sensors. This WILL solve alot of idle problems. You may not necessarily get a CEL, even though the sensor could be sending out bad data.

 

[CivicEater]

I noticed today that my A/F guage rides on RICH to the extreme after the car is first started then after a few miles it usually goes to the middle ground.....that yell ECT?

 

[96darkhorse]

ohh yeah...other symptoms that i get as well that i forgot to state is that the car once in a while pinges. sometimes i get a big amount fuel smell at a stop, and when i take my foot off the accelerator, it bucks or actually it feels like the car pulls back.....i hope its the IAC....im gonna go get it on fri

 

[mo_dingo]

"He said the idle speed problem was exactly the same no matter if the car was hot or cold. That rules the ECT out. A bad ECT would make the car run richer than hell, and trigger a CEL."

Absolutely WRONG,WRONG,WRONG!!! A bad ECT could cause the car to run rich OR lean. Also,it may not trigger a CEL.

For the sensor to cause a SOMEWHAT SERIOUS idle/driving issue, it needs to completely die. My brothers ECT sensor went out completely on his 90 bronco (5.8L), reading no resistance no matter what the temp was. The Bronco ran almost perfect except a small amount of black smoke came out the tailpipe. So his sensor was COMPLETELY DEAD (Codes present), and the engine still ran well. You are talking about a very small variation too lean, or too rich; Either way, the ECT isn't the MAIN cause of his problems.

So, I say ONCE AGAIN, if you're IAT/ECT sensors are old, REPLACE THEM with new Ford sensors. This WILL solve alot of idle problems. You may not necessarily get a CEL, even though the sensor could be sending out bad data.

Sorry, you are WRONG WRONG WRONG WRONG WRONG WRONG WRONG WRONG WRONG WRONG WRONG
. The IAT/ECT BEING SLIGHTLY OFF WILL NOT SOLVE [size=+4]MAJOR[/size] idle issues. Only small ones!!!! The damn sensor would have to be completely dead, which would trigger a CEL.

Back to the correct diagnosis.

The IAC only controls the AMOUNT of air that enters into the engine AT IDLE SPEEDS ONLY. Once you open the butterfly, it's purpose is gone. The only way the IAC could have anything to do with this situation would be if the IAC was loose, or the gasket inbetween was completely shot, causing a vacuum leak.

From you last post, it sounds like you are running rich when at idle, and running lean while driving, I assume? Sounds exactly like a MAF sensor. There are tables that relate the voltage output vs. CFM intake of the motor. I will see if I can find them in one of my books. I will post back later.

Have you ran the engine codes yet? If you haven't, that is the first thing you should do.
Go here

Once you have ran the codes, report back here before you go buy useless parts.

My guess is a code has been set off, but the computer can adapt somewhat, so the CEL won't stay on 24/7.

Note: Sorry for the sarcasm and spite. I hate when people make BOLD statements when they don't have any Fu *king clue what they are talking about.
Scott

 

[Silver85TC]

Mo Dingo

WTF is your problem? You are the end all be all expert on Ford EEC? LOLOL I highly doubt it.

I'm making my post from my own experiences with rough idle/hanging idle etc. and how I SOLVED the problems. What is your experience solving these problems?

Quote:
The IAT/ECT BEING SLIGHTLY OFF WILL NOT SOLVE MAJOR idle issues. Only small ones!!!! The damn sensor would have to be completely dead, which would trigger a CEL.


Once again you are absolutely incorrect. Just after I bought my 86 Gt. I was having all kinds of bad/rough idle/hanging idle problems (I'm talking hanging at 1800 rpms at a stop light.....very annoying). I did all the usual stuff...ran codes...nothing....complete tuneup(plugs/wires/cap/rotor/cleaned IAB valve etc)....helped a bit, but not solved completely...idle was still hanging intermittently. I then decided to change the ECT/IAT sensor's as they looked to be original (15 years old at the time...no trouble codes were present).
Problem solved!!!! Very SMMOOOOOOOOOTH idle (I'm talking honda smooth).....idle speed was rock steady at 700 RPM.....no more hanging idle!!!

Now, as other people have mentioned, you must trouble shoot before randomly changing parts. First thing is to run codes. If no codes are present, then make sure your tuneup is fresh..... plugs, wires, cap, rotor, clean IAB valve, throttle body, MAF meter etc. If you've already done all that, then you have to start looking at sensor's. Do a search on this site. The spec ohm's/voltage output for various sensor's has been posted many times in the past. If all the sensor's are within spec, then look at the sensor wiring. If the sensor's/wiring check out ok, then start looking at the injector's......you get my point. Approach the problem with patience and logic, and you WILL solve the problem.
I'm not saying that changing your sensor's will be a 100% guarantee that your idle problems will be solved, BUT, if you're sensor's are old/original they will not be nearly as accurate as a brand new sensor would be. It is a well documented fact (do a search on this site and you'll see) that sensor's can be off by quite a bit and still not throw a CEL.

In closing.

Quote:
I hate when people make BOLD statements when they don't have any Fu *king clue what they are talking about.


My sentiments exactly.

 

[Silver85TC]

ohh yeah...other symptoms that i get as well that i forgot to state is that the car once in a while pinges. sometimes i get a big amount fuel smell at a stop, and when i take my foot off the accelerator, it bucks or actually it feels like the car pulls back.....i hope its the IAC....im gonna go get it on fri

96darkhorse,
As you mentioned that your car was pinging, it reminded me of another poster who had major pinging problems. He solved the problem by changing the ACT sensor (it was faulty, but wasn't throwing a code...gee, havn't we discussed this before? ).
Have a look at the thread. It brings up some very good technical info.

http://forums.stangnet.com/showthread.php?t=345453&highlight=Pinging

Hope that helps

 

[revhead347]

Refer to my earlier post which corresponds this particular symptom to my past experience.

Kurt

 

[mo_dingo]

Mo Dingo

WTF is your problem? You are the end all be all expert on Ford EEC? LOLOL I highly doubt it.

My problem was you responded to one my posts with "you are WRONG WRONG WRONG,"...etc, so I decided to do the same. Arrogance is annoying at times.

I'm making my post from my own experiences with rough idle/hanging idle etc. and how I SOLVED the problems. What is your experience solving these problems?

My experience in solving these problems was CLEARLY stated in my last post (working on my brothers 90 351W bronco). Also from working on my car. My idle hung at 2200 rpm's, and I replaced my IAC valve and everything was peachy keen.

Quote:
The IAT/ECT BEING SLIGHTLY OFF WILL NOT SOLVE MAJOR idle issues. Only small ones!!!! The damn sensor would have to be completely dead, which would trigger a CEL.


Once again you are absolutely incorrect. Just after I bought my 86 Gt. I was having all kinds of bad/rough idle/hanging idle problems (I'm talking hanging at 1800 rpms at a stop light.....very annoying). I did all the usual stuff...ran codes...nothing....complete tuneup(plugs/wires/cap/rotor/cleaned IAB valve etc)....helped a bit, but not solved completely...idle was still hanging intermittently. I then decided to change the ECT/IAT sensor's as they looked to be original (15 years old at the time...no trouble codes were present).
Problem solved!!!! Very SMMOOOOOOOOOTH idle (I'm talking honda smooth).....idle speed was rock steady at 700 RPM.....no more hanging idle!!!

Think about this logically. The IAT/ECT ONLY tells the comp how much fuel to add/remove. They in no way affect regular idle speed. If the engine idled steady @ 1800, then my guess was your IAC was the culprit, and cleaning it out actually fixed it. When you cleaned the IAC, did you drain the power from the system and reconnect? Did you only do it when you did the ECT/IAT?

I'm not saying that changing your sensor's will be a 100% guarantee that your idle problems will be solved, BUT, if you're sensor's are old/original they will not be nearly as accurate as a brand new sensor would be. It is a well documented fact (do a search on this site and you'll see) that sensor's can be off by quite a bit and still not throw a CEL.

That is correct, the computer only tells you when a sensor completely dies(i.e. reads 5 Volts or 0 Volts), or it cannot control the fuel mixture/etc. by compensating.

Scott

 

[Silver85TC]

Ref your problem;

He said the idle speed problem was exactly the same no matter if the car was hot or cold. That rules the ECT out. A bad ECT would make the car run richer than hell, and trigger a CEL.

That statement is just plain wrong. I explained why you were incorrect in my earlier posts. You were very "matter of fact" in this statement. Hence the wording "wrong, wrong, wrong."

Arrogance is annoying at times.

I agree with you on that one.

My experience in solving these problems was CLEARLY stated in my last post (working on my brothers 90 351W bronco).

You also stated you had a trouble code present....good troubleshooting on that one.

Also from working on my car. My idle hung at 2200 rpm's, and I replaced my IAC valve and everything was peachy keen.

I don't dispute that a faulty IAC valve would cause major idle problems.

The IAT/ECT ONLY tells the comp how much fuel to add/remove.

Partially correct. The comp also adjusts timing based on the temp.

They in no way affect regular idle speed.

Indirectly, they will. Consider the following;
The actual temp is 15 deg Celcius. The ECT is sending out the maximum cold temp that would NOT set off a code (around -40 believe... can't remember the exact temp). The ACT sensor is sending the correct temp. The comp adds fuel/adjusts timing for a -40 deg engine. Obviously the air/fuel ratio is going to be way too rich and the car will run like crap. Comp senses crappy idle through PIP sensor and tries to impove it by increasing airflow a bit with the IAC valve. (would also sense rich condition once O2's warm up)The precalculated adjustments are off because of the faulty sensor, so the IAC valve opens up too much.....high idle.

Now consider if both sensor's are faulty. One sensor is sending the lowest temp that would set not set off a code and one sensor is sending the highest temp that would not set off a code. The car is running really $hitty now and the comp is trying to adjust the idle with the IAC valve (idle starting to wander/too high).

Now consider a sensor that is sending out random voltage, yet not outside the parameters that would trip a code. (don't believe this is possible? Ask any electronics guru/electrical engineer about old thermistor's) The comp will now be "chasing" the idle by continuously adjusting the IAC valve, generally causing the idle to really start to wander. (roving idle)

Most electronic devices don't hold up well after 10+ years in an environment with vibration and extreme heat changes. The sensor's are quite inexpensive and easy to change (5 minutes each). So why not change them out if you are in doubt?

If the engine idled steady @ 1800, then my guess was your IAC was the culprit, and cleaning it out actually fixed it. When you cleaned the IAC, did you drain the power from the system and reconnect?

I didn't say the engine idled CONSISTANTLY at 1800 RPM's. It ranged from normal idle UP TO 1800 RPM's. I always disconnect the battery for 30 min after I perfom any tuneup item. In this case, I had reset the comp numerous times after I tried different things to get the idle under control. (clean IAC valve, new plug wires/cap etc.) The idle only returned to normal after replacing both the ECT and ACT sensors (I changed them at the same time). Both my stangs now idle/run like new cars. Changing the ECT/ACT sensors was the solution. Period.


In summary, you can't make these blanket statements that are incorrect and not expect people to call you on it.

If you are searching for the answer to a difficult problem, have patience and be open to new information and ideas. You will start thinking about things differently and find the solution. ( Woah! that was zen-like!! )

 

[Silver85TC]

96darkhorse,

Sorry for semi hi-jacking your thread.
I'll shutup now as everyone obviously knows my postion.
Let us know how things are progressing.

Goodluck

 

[Silver85TC]

Sorry, I lied!

One more post.

If you want to check your ECT sensor output yourself, I found a complete temp range chart comparing temp with voltage/resistance on the Ford Fuel Injection website under sensor's/ECT. Look at the bottom of the page.

http://fordfuelinjection.com/ect.html

Cheers.

 

[ShiftTheDrift]

Hey guys, where exactly is the ACT and ECT sensors located?

 

[Silver85TC]

The ACT sensor screws into the air inlet tube right after the MAF meter.

The ECT sensor screws into the hard coolant line between the distributer and the alternator.

You'll need a 1" deep socket to remove them.

 

[ShiftTheDrift]

Thank ya much!

 

[96darkhorse]

ok...here is some other stuff i keep forgeting to tell you guys...once i turn on the car, the CEL light is on.....it starts idling at 500 rpm then it will jump to 1200, then it will go down again to 500 then again to 1200rpm and it will keep on doing that......sometimes it will do that at every stop light but sometimes the idle will just hang at 1500rpm...most of the time i let off the gas pedal ill feel like a little buck or more like it pulls back, like if it needs air....i know i posted this a week ago..but i havent been able to tackle the problem because of work ....i have the new iac valve but i just havent been able to put it on....i hope this cures the prob

 

[mo_dingo]

ok...here is some other stuff i keep forgeting to tell you guys...once i turn on the car, the CEL light is on.....it starts idling at 500 rpm then it will jump to 1200, then it will go down again to 500 then again to 1200rpm and it will keep on doing that......sometimes it will do that at every stop light but sometimes the idle will just hang at 1500rpm...most of the time i let off the gas pedal ill feel like a little buck or more like it pulls back, like if it needs air....i know i posted this a week ago..but i havent been able to tackle the problem because of work ....i have the new iac valve but i just havent been able to put it on....i hope this cures the prob

So your idle speed will occasionally stay steady at 1500 rpm's? Hmmmm....

I still don't think it's the IAC valve, but you can try. If it doesn't fix your problem, then take it back.

The IAC valve I bought at Autozone would not work for my car. There was a little piece of paper at the bottom of the box, that said the new IAC needs to be mounted opposite of the original position (180*).

Problem is that the Oil fill tube prevents this from happening, so the part cannot be mounted 180*.

If you got a Borg Warner one (I got mine @ Pep Boys), it will look extremely similar to the original one, and that is the one that will work. No need to mount 180*.

here is some other stuff i keep forgeting to tell you guys...once i turn on the car, the CEL light is on

So after you start the car, the CEL light stays on? Before you start the car, stick the key in the ignition, and turn the key foward to acc. mode (one position before the starter will engage). The CEL light should come on, and stay on. Now, start the car. After the car is started, does it stay on?

If it stays on, that means the computer knows something is wrong, and is telling you to pull the codes. Here is a link to instructions & a code breakout listing. It tells you how to run the codes. But get you Haynes manual, and use the steps it lines out there to do the test.

In place of a "code scanner", you put a jumper wire in it's place, and watch the CEL light flash, and the flashes correspond to engine codes.

Let us know what happens.
Scott

 

[FastGT94]

I'm having the same problem after a H/C/I problem and bought both new sensors (IAC and ECT) I still have the old ones which were working fine before I tore things apart. I'm going to replace both of them and let you guys know if it fixes anything.

 

[mackey]

Sorry, you are WRONG WRONG WRONG WRONG WRONG WRONG WRONG WRONG WRONG WRONG WRONG
. The IAT/ECT BEING SLIGHTLY OFF WILL NOT SOLVE [size=+4]MAJOR[/size] idle issues. Only small ones!!!! The damn sensor would have to be completely dead, which would trigger a CEL.

Back to the correct diagnosis.

The IAC only controls the AMOUNT of air that enters into the engine AT IDLE SPEEDS ONLY. Once you open the butterfly, it's purpose is gone. The only way the IAC could have anything to do with this situation would be if the IAC was loose, or the gasket inbetween was completely shot, causing a vacuum leak.

From you last post, it sounds like you are running rich when at idle, and running lean while driving, I assume? Sounds exactly like a MAF sensor. There are tables that relate the voltage output vs. CFM intake of the motor. I will see if I can find them in one of my books. I will post back later.

Have you ran the engine codes yet? If you haven't, that is the first thing you should do.
Go here

Once you have ran the codes, report back here before you go buy useless parts.


Note: Sorry for the sarcasm and spite. I hate when people make BOLD statements when they don't have any Fu *kMy guess is a code has been set off, but the computer can adapt somewhat, so the CEL won't stay on 24/7.
ing clue what they are talking about.
Scott

Actually if your IAT is not working correctly, or you have a wire that is worn out (like I did) the cars idle will surge and sometimes it will even stall out. I hate people without experience making stupid statements when they have never even had a problem with that part of their car even though they are trying to help.