VERY unusual idle behavior.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
VERY unusual idle behavior.
Just finished my new 383 and it will start and run but I cannot get it to idle. I have done the minimum air idle adjustment many times trying to figure this out. First of all, I do not believe it is a vacuum problem. I used a cigar to fill the manifold with smoke through the large port on the driver's side. The only place smoke came out was the air filter housing. The smoke made it from the manifold up through the runners and plenum and out the throttle body. I tried it again while holding my hand over the throttle body and still no smoke anywhere until I removed my hand. I could even feel pressure against my hand when I was blowing into the manifold. The IAC is working correctly, I verified this visually, also the IAC circuit is working, verified by a noid light. When I set the base idle and reconnect the IAC it is not too bad but when I shut the engiune off and restart the rpm's go to 1100-1200 and hold there steady. When I put it in gear the rpms drop down to 790-800. Could this be the ECM? I have had this problem prior to the rebuild just not to this extreme extent. I'm completely at a loss so any ideas/help is appreciated.
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
Did you also set the TPS and timing? If the ECM thinks the throttle is open, it'll add timing and fuel. Speaking of which - is the chip stock? If so, that'll cause some headaches.
A scanner would help to verify the target idle and the IAC pintle steps. However, the ECM would not know if the IAC pintle is actually moving properly. Have you cleaned the throttle body and IAC motor lately?
The 383 will only amplify the problem you had prior to installing it. I doubt it's the ECM, though.
A scanner would help to verify the target idle and the IAC pintle steps. However, the ECM would not know if the IAC pintle is actually moving properly. Have you cleaned the throttle body and IAC motor lately?
The 383 will only amplify the problem you had prior to installing it. I doubt it's the ECM, though.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Timing at 6* advance with EST disconnected and with idle varying between 490 to 510.
TPS set at .560, throttle body clean as a whistle. Chip is not stock but is the same one I had before rebuild and was added after the problem first showed up. Please explain how this or the fact that it's now a 383 would amplify the problem.
TPS set at .560, throttle body clean as a whistle. Chip is not stock but is the same one I had before rebuild and was added after the problem first showed up. Please explain how this or the fact that it's now a 383 would amplify the problem.
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
The addition of 33 cubic inches by itself wouldn't really amplify the problem; I had (wrongly?) assumed that there were other modifications such as a bigger cam, injectors, etc which would. I should have asked in my first post, but I'll ask now - what other mods (intake, cam, injectors, etc) have been done to the engine and what chip are you currently using? :o
If the TPS is properly reporting .54 volts at idle, then you should be ok there.
If the TPS is properly reporting .54 volts at idle, then you should be ok there.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
The addition of 33 cubic inches by itself wouldn't really amplify the problem; I had (wrongly?) assumed that there were other modifications such as a bigger cam, injectors, etc which would. I should have asked in my first post, but I'll ask now - what other mods (intake, cam, injectors, etc) have been done to the engine and what chip are you currently using? :o
If the TPS is properly reporting .54 volts at idle, then you should be ok there.
If the TPS is properly reporting .54 volts at idle, then you should be ok there.
I am 99.9% sure I can eliminate vacuum leaks because of tests I did described in my first post. The fact that the idle changes so much when I put it in gear is what is making me think ECM. I had the throttle body off so I took off the bottom bypass/IAC cover and keyed the ignition. The IAC was open when I did this and it closed immediately.
I tested the IAC circuit with a noid light and when I turned the ignition on I had a red and green light, I started the engine and the lights went red, after a few seconds they went green, then back to red/green and went on with a pattern like this. My noid light set doesn't tell me what is normal light pattern so I'm guessing that the different patterns are happening when the IAC is moving in or out.
Normally I refuse to throw parts at it but I'm about ready to order another ECM.
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
If the chip from Jesse made it better, then I doubt it is the ECM. Changes he made to timing, fueling, etc were probably enough to mask some of the problem, though.
Can you get it to run long enough to go into closed loop? Does it do this in both open and closed loop?
Can you get it to run long enough to go into closed loop? Does it do this in both open and closed loop?
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Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Okay, I don't know which one of you guys snuck in my garage last night and fixed my problem but I went out in the garage today, fired it up and it is purring like a kitten. I really don't know what to think, I know a shutoff and restart is necessary but I had already done that.
byebyeL98 and AGENT 86, I want to thank you for your responses and ideas. BTW I think this 383 is going to be LOTS of fun.
byebyeL98 and AGENT 86, I want to thank you for your responses and ideas. BTW I think this 383 is going to be LOTS of fun.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
wierd
ok, this is going to sound wierd....
I put new injectors in my car, and when I first started it up, it would run ragged, and idle like it had bad plugs.
I went to the guy that sold me the injectors, and he said they put a preservative on the injector seats because of un known shelftime.
maybe the perservative was holding the injectors off their seats a little, and the iac was adding air to compensate, and the computer was scaling back the injectors.
you let it sit overnight, and the gasoline softened up the preservative, the injectors seat, and now everything is fine?
just my 2c worth
I put new injectors in my car, and when I first started it up, it would run ragged, and idle like it had bad plugs.
I went to the guy that sold me the injectors, and he said they put a preservative on the injector seats because of un known shelftime.
maybe the perservative was holding the injectors off their seats a little, and the iac was adding air to compensate, and the computer was scaling back the injectors.
you let it sit overnight, and the gasoline softened up the preservative, the injectors seat, and now everything is fine?
just my 2c worth
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Injectors were the same ones I had in before the rebuild but I wonder if they formed a varnish on the tips while they were in storage. Interesting bit of info, thanks.
Instructor
Joined: Jun 2006
Posts: 128
Likes: 0
You need to drive and let the ECM "relearn" the idle.
Have you tried this. It takes multiple speed ups and decels. I don't recall the exact procedure but give it a shot. Have you driven it?
Be sure to use the A/C. It will relearn it's idle also.
Later.
Have you tried this. It takes multiple speed ups and decels. I don't recall the exact procedure but give it a shot. Have you driven it?
Be sure to use the A/C. It will relearn it's idle also.
Later.
Race Director
Joined: Aug 2000
Posts: 14,130
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Cruise-In II Veteran
Glad to hear you got it fixed! Btw,anytime you do a minimum air speed adjustment,or set the iac and tps,you should drive it right away and get the car to 40+ mph...that helps to reset the IAC valve.If im wrong,someone point it out..it has been a while since I fooled around with that TPI settings...I think starting,shut down and restarting has the same effect sometime.I went through something similar before.Maybe your start and restart a few times set it back to normal.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Glad to hear you got it fixed! Btw,anytime you do a minimum air speed adjustment,or set the iac and tps,you should drive it right away and get the car to 40+ mph...that helps to reset the IAC valve.If im wrong,someone point it out..it has been a while since I fooled around with that TPI settings...I think starting,shut down and restarting has the same effect sometime.I went through something similar before.Maybe your start and restart a few times set it back to normal.