HELP BAD IDLE!!! Please for the love of god

[raininfire]

I have been battling a bad idle for the last 4 months. I just want to drive the damn car without getting pissed off. Here's what it is doing: it randomly idles high at around 1500-2000rpm's, then it goes down to 750 sometimes. The idle will also wander from 1000-1100, making it eractic when your driving (jerky).
When ever I replace a part it will go away for a few days, then come back after I thought I finally fixed the problem. Things I have fixed:
1. Bought new IAC/IAB valve on throttlebody
2. Cleaned throttle body
3. Took cold air out and replaced with stock airbox
4. Cleaned MAF sensor
5. Cleaned salt and pepper shakers
6. Cleaned PCV valve
7. TPS sensor is 1 year old

Any opinions, I am getting really frustrated. I was thinking maybe the MAF needs to be replaced. Thoughts???

 

[bubba-dough]

Have you pulled any codes?? http://forums.stangnet.com/showthread.php?t=534062

 

[HISSIN50]

Have you read through JRichker's sticky at the top of the page? It covers just about every possibility out there.

Good luck.

 

[raininfire]

I haven't checked the codes, I have seen that link before and thats were I started doing the "checklist." But I will look into the codes thing right now. Thanks. Anyone else? I will definately buy you a 6 pack if u live in the area.

 

[ss93cobra]

Just a thought, try disconnecting the m.a.f. and see if the idle straightens out

 

[Desert Stallion]

Disconnecting the MAF will probably make the car wuit running...

What's the TPS voltage at idle? Have you put a vac gauge on the car or searched for a vac leak?

 

[Swarzkopf]

1. Reset the car's ECU. Disconnect the car's negative battery cable and leave it disconnected for 30 minutes.
2. Check for a vacuum leak.

 

[2002BLGT]

pull the upper intake off the car and trace down every vacuum line coming off of it ....sounds like a vacuum leak to me

 

[raininfire]

I will see if I can trace any vacuum leaks, but I didnt "hear" any before, unless they are not that noisey. I have reset the ECU as well last week when I put new O2 sensors in.

 

[Desert Stallion]

You won't always hear a leak. That's what's fun about them. A good hunting tool is a can of carb cleaner that you can spray into areas where a leak might occur. If the engine revs up when you spray an area, chances are you've got a leak there.

 

[DMAN302]

The vac lines are very tricky...I checked the bay over a damn near a dozen times after the engine was installed, traced every line (I thought), then one beautiful sunday morning I found a broken line just inside the passenger side fenderwell at the vac canister behind the strut tower near the firewall. One of those gay little hard plastic lines being broken can reak havoc on the idle..keep looking. Also check your O2 sensor heater ground..hego wire coming off the harness on the back of the engine (orange wire) by the firewall.

 

[raininfire]

One of those plastic lines are broken, could that be the problem, currently I have it tapped together. It is on the passenger side, to the left and down of the throttle body. Gonna go check that now.

 

[Darkwriter77]

This may sound odd, but you might wanna have your TFI module tested, too. The last battle I had with weird idle issues, stalling, and surging turned out to be that. Places like Napa and Autozone can bench-test it for free ... although it can show up as "good" sometimes when it's not. (Have them run the test, like, six or so times in a row so that the module heats up.)

I agree, it sounds like a vacuum leak, but if you have a warranty on the IAC you bought, I'd try having them swap that out for you. Sometimes you can get a bum unit right outta the box.

 

[DMAN302]

You may need to reset the idle again after fixing the vac leak..by attempting to correct it previously with things out of whack you may need to go throught the idle set proceedure from corral.net
http://www.corral.net/tech/maintenance/idlereset.html
I wish you the best..been there.

 

[MatthewP]

I've seen the EGR valve have a tear in the membrane and cause a vacuum leak inside the valve. Check for this by pulling the line off the valve and plugging it. It's a bit of a long shot, but not something you normally think of checking.

-Matthew

 

[HISSIN50]

One of those plastic lines are broken, could that be the problem, currently I have it tapped together. It is on the passenger side, to the left and down of the throttle body. Gonna go check that now.

Yes that can cause some funky issues. I just broke one myself. You can buy it in bulk at the parts store (Thanks MM for that tip - I never could find it before). Or in my case, I just used a small splice of rubber line to reconnect the broken hard line.

Good luck.

 

[Skoobie]

Use a vac guage...its a little more accuate than listening for a leak. Normal hg should be in the 16-22 range. Unless your running a cam then it may be lower (Im running 12-13 on an E cam right now). Just make sure its steady. Rev the motor and see what happens to the reading. My guage came with a cool guide that told you what the #'s ment as far as a burnt valve, vac leak, so on and so fourth.

::EDIT:: I noticed you replaced your CAI with the stock AB, I didnt know this was a fix? A CAI can cause a searching/rough idle???

 

[raininfire]

The reason I changed back to the stock airbox was because I heard with certain MAF units, I have a C&L set for 24lb injectors that a cold air intake can "mess" with the readings. I tried clocking the maf and it did nothing. So I said f it I am going back to the stock box, and the funny thing is, problem went away for a few days. My car never stalls, it just randomly will idle high. I fixed the leak tonight, I got a car show tomorrow, so I will see if that did it or not.

 

[raininfire]

Oh ps, I do most of the work on my car myself, however I am working 2 jobs and finishing my last semester at school. So to try some of these things out I just can't get around to it. I would hate to take it to a mustang shop for them to tool around on, but if they fixed the problem I would be happy to pay. I wonder if it would cost an arm and a leg to get this worked out?

 

[legalize420]

did you put your stock injectors back on?