2000 GT - Motor randomly dies with Heater set on Defrost.

[jayrw]

Whenever I use the defrost setting on my heater (to clear foggy windshield) it causes the motor to have random loss of power (kind of a bucking sensation) also when I come to a stop the idle will go up and down along with the motor dying altogether at random times, It died on me 3 times today.

With the heater off the car runs fine, no bucking ,dying or erratic idle.

Any ideas appreciated.

Motor is stock, 75k miles.

 

[wmburns]

Does the AC work? Does this problem happen at idle? Check the Serpentine belt. Look for evidence of slipping. Watch the belt tensioned and see if it adjusting constantly.

If the lights are turned on while this happens are the bright and constant?

Possible that the IAC is not working. What does the idle do when the AC is turned on/off?

Also possible that the electrical load is excessive. Causing the voltage to drop. Can you measure the voltage while this is happening?

 

[trinity_gt]

I agree with the A/C and IAC angle. In defrost, the A/C cycles to dehumidify the air before it's blown on the windshield. The A/C compressor presents a fairly significant load to the engine when activated and the PCM should compensate with a bit more idle air. If the IAC valve is malfunctioning you may not be getting this additional air and the motor may have idle issues.

Any work done around the throttle body or IAC lately? You may also want to check for vacuum leaks.

 

[wmburns]

I was even thinking that the AC compressor is totally frozen up (didn't want to jump there straight away). When the AC kicks on, the engine is presented with a huge load that is above what can be adjusted for.

Another angle is there is a feed back from the alternator to the PCM. The PCM will increase the idle speed when the alternator load suddenly increases. This prevents idle surge when loads turn on/off.

Check the small wires to the alternator. IMO, this is a long shot as I would expect that the battery charge light would also come on.

Yet another angle is belt slipping to the alternator when the electrical load increases above a certain point. It's easy to see how a reduction in electrical voltage can cause problems.

In several of the cases, the IAC could still play a role.

 

[2000GTdriver]

My 2000 GT does the same thing so post your solution if you fix it please. Good luck ...

 

[wmburns]

My 2000 GT does the same thing so post your solution if you fix it please. Good luck ...

so why not check the same things on your car? Might be different. Might offer different insight.

 

[myponyrocks]

Mine did this after a mail order tune, turned out they'd set the idle too low. Maybe you've done something similar? If so bump the idle back up a bit. If not then I'd lean towards IAC or dirty MAF.

 

[2000GTdriver]

so why not check the same things on your car? Might be different. Might offer different insight.

More info: AC was working and all belts were fine when the surging problem started. I posted it in tech here and asked for help from whoever had acually had this problem and fixed it. A few people said to just buy a new IAC but I never got an answer from anybody with actual exprience. So before I spend a hundred bucks on a part that may or may not be the cause, I am still hoping to hear from somebody who had the same problem and fixed it.

 

[wmburns]

To check the IAC (free). Remove the electrical connection, if it dies right away, the IAC is basically working. If it continues to run, there is either a vacuum leak or the IAC is not working.

Monitor the IAC percent with an ODB2 scanner. Turn the AC on and off and verify the IAC percent changes and the idle is good. Also monitor the RPM. Shouldn't vary by more than say 100RPM.

Note, the IAC goes bad a lot. Often ppl will try to clean it. However, experience has shown that to be a temporary repair at best.

And last but not least, the old standby, check for vacuum leaks and clean the MAF.

I don't see anywhere in my posts saying to replace anything. Lots of check this, check that.

 

[jayrw]

Sorry for the lack of replies, (don't you hate that) anyhow I appreciate the suggestions and I will be looking at it soon, Ive been so busy at work I haven't had time to check it out.

The AC works but also causes erratic idle, the weird part is the erratic idle only occurs if I have the fan speed set on the lowest setting while AC is on, weird eh?

I had the intake manifold replaced recently (cracked) but all these symptoms were occurring before it was replaced as well.

 

[patman0911]

Sorry for the lack of replies, (don't you hate that) anyhow I appreciate the suggestions and I will be looking at it soon, Ive been so busy at work I haven't had time to check it out.

The AC works but also causes erratic idle, the weird part is the erratic idle only occurs if I have the fan speed set on the lowest setting while AC is on, weird eh?

I had the intake manifold replaced recently (cracked) but all these symptoms were occurring before it was replaced as well.

Get out there and check it! Some of this stuff you can check during a smoke break - disconnecting the IAC connector while running, watching the belt tensioner during defrost or A/C cycles and hooking up a scanner (if you have or have access to one).

 

[jayrw]

Get out there and check it! Some of this stuff you can check during a smoke break - disconnecting the IAC connector while running, watching the belt tensioner during defrost or A/C cycles and hooking up a scanner (if you have or have access to one).

So today I finally decided to try something lol..

When I unplug the IAC with the car running (car had been drivin for awhile so motor was warmed up) the car continues to run but at a much lower idle rpm (right around 400-500rpm) im able to rev up the motor and it'l return to this low idle, I then reconnected the IAC and idle returned to normal, would this indicate a properly working IAC? or possibly a vacuum leak?

 

[wmburns]

bad AC diode?

The drop in RPM indicates that the IAC is working. Note, if your car has an IAC with a black vent, the idle will slow. Without the IAC, the motor should quit.

Was reading the shop manual and it listed a bad AC diode as a possible source of a rolling idle. I suspect that what happens is the diode limits the current in-rush as the AC clutch engages/disengages.

On my own 2000 GT would die when cold coasting up to a stop. It passed all IAC tests and was apparently fine. However, once the IAC was replaced my problem when away.

 

[jayrw]

The drop in RPM indicates that the IAC is working. Note, if your car has an IAC with a black vent, the idle will slow. Without the IAC, the motor should quit.

Was reading the shop manual and it listed a bad AC diode as a possible source of a rolling idle. I suspect that what happens is the diode limits the current in-rush as the AC clutch engages/disengages.

On my own 2000 GT would die when cold coasting up to a stop. It passed all IAC tests and was apparently fine. However, once the IAC was replaced my problem when away.

Hm so AC diode perhaps..Is that an easy part to replace?

I also noticed while I had hood up (engine idling) the cooling fan kicked on and it caused engine rpm to drop pretty low for a brief second. (IAC was still plugged in).

And a couple of other observations while I had the hood up today....

Im hearing a pretty noticeable rapid ticking sound coming from top end of motor during engine idle... its not a deep sounding tick its more like a light metallic ticking sound (Rapid), is this a noisy valve train perhaps? I cant hear it while hood is closed. I can record a video tomorrow maybe that will help..

And last but certainly not least the motor has a rough idle, especially after warmup, You can see the motor slightly shaking with the hood up but it feels smooth when I rev engine. I cleaned the MAF with crc maf cleaner a couple weeks ago but it didnt seem to help anything. (rough idle has been going on for several months).

Any ideas / thoughts appreciated, and I promise not to abandon my thread again lol.

 

[jayrw]

I just recorded some video of the motor running w/ hood up (ticking sounds) and im also concerned about a random low "pop" sound coming from the exhuast during idle... I recorded that to, i have to leave for work now so no time to upload but I will post a link later tonight..

 

[Midnight2V]

I'm thinking its a vacuum leak. My car did the exact same thing. Turned out to be a broken vacuum line off of the climate control module in the engine bay passenger side just in front of the firewall.

 

[jayrw]

Ugh I just downloaded the video from my camera and the motor sounds horrible(?!) It sounds like a diesel engine lol, The camera seems to be exaggerating the noise a little but Is it possibly a timing chain issue? Also towards the end of the video you can hear the low "pop" sounds coming from exhaust, despite all this the car still has a decent amount of power.

But I obviously need to address these issues, I always keep up on the oil changes / filters every 3k miles and I checked the oil level before recording this video.

Any ideas appreciated

http://ded.zenblue.net/2000GT_Noisy.AVI (17.5MB file, standard .AVI format straight from camera) Unfortunately camera only records video at 320x240.

Engine is all stock with 77K miles and a centerforce dual friction clutch.

 

[jayrw]

Anyone?

 

[patman0911]

Ha ha, it does sound like a diesel - it's probably not that bad though. It's hard to tell from the video, digital cameras just distort so much and the frequency response is awful so it probably is exaggerating the noises in the midrange a lot.

A lot of tapping noise is probably just the injectors - they just naturally make a lot of noise - and it seemed to get more prominent when you got near the valve covers. There did seem to be some noise from the front of the motor when you got down near the passenger cam gear but it's hard to tell if it's just normal pulley & chain noise or something more.

The occasional random pop in the exhaust at idle is fairly normal but a vacuum leak or other problem affecting idle quality could make it more frequent as the PCM can't accurately control the engine at idle and you get occasional misfires .

You said the RPM's dropped really low when the cooling fan came on? The PCM should try to maintain or increase RPMs under a heavy electrical load - perhaps despite passing the quick test, the IAC is only partially functioning.

 

[dangrus]

My 2000 was having a similar issue, while cruising you could feel the A/C compressor cycling on and off. When it kicked on, you could feel the car slow down. At idle it would almost kill it.

I ended up replacing the lines to get to the orfice filter, and the low/high pressure cut off switch. I don't know if the filter cause the sensor to go bad, but the sensor was constantly cycling the compressor. It got so bad that I quite running the A/C in the middle of summer. The lines cost about $200 or so to replace, and the sensor was like $150 or so, both were done at different times so I had to pay for 2 different evacuation/recharges.

I think this happened when I had about 80K on it.

Hope this helps.