88 idles too low
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 3,151
Likes: 294
From: Opelousas, Lousiana
CI 6-7 & 9 Veteran
88 idles too low
I'll try again.
My 88 35th annerversity special (equipped with 4 speed automatic) seems to idle too low (500 RPMs) when at a red light or stop sign after the car has warmed up. This causes the alternator to only put out about 11.5 volts. It does not dies but occasionally will hesitate when I take off. I thought the fuel filter might be bad so I replaced it. This did not solve the problem. The Car runs fantatic when it is not at idle speed. She has only 48K original miles. The car had recieved a minor tuneup @ 43,000 when the distributer cap was replaced and the plugs and wires were checked.
Any ideas?
My 88 35th annerversity special (equipped with 4 speed automatic) seems to idle too low (500 RPMs) when at a red light or stop sign after the car has warmed up. This causes the alternator to only put out about 11.5 volts. It does not dies but occasionally will hesitate when I take off. I thought the fuel filter might be bad so I replaced it. This did not solve the problem. The Car runs fantatic when it is not at idle speed. She has only 48K original miles. The car had recieved a minor tuneup @ 43,000 when the distributer cap was replaced and the plugs and wires were checked.
Any ideas?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Even with a non firing cylinder (assuming compression is normal), it should maintain idle speed. I'd scan it and see what the the ECM is targeting for rpm. Actual should be within 50 rpms of that # in Drive, 100 rpms in neutral or park. Check IAC counts - 12 to 15 with the a/c off. My guess would be that the IAC is funky or the air passage is dirty - clean the throttle body.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
You can try cleaning the IAC and the passage it screws into with some carb cleaner and an old toothbrush. I clean mine that way and it DOES make a difference, even though some claim they cannot be cleaned, only replaced.
I just cleaned mine a couple of weeks ago and the difference was immediately noticable.
You can actually remove the pintel from the IAC by pulling on the tip while rocking it from side to side. Reinstalling it is just the reverse.
The idle speed is controlled by what's burned in the PROM; raising it calls for a PROM re-burn. Some resort to using the minimum airflow screw on the throttle body to raise the idle speed, but this isn't the right way to go about it. Using that technique effectively causes the IAC pintel to completely extend, closing off any air it would normally contribute to maintain idle speed.
You'll need a ScanTool or Diacom, etc., to see what the Command Idle Speed is.
Jake
I just cleaned mine a couple of weeks ago and the difference was immediately noticable.
You can actually remove the pintel from the IAC by pulling on the tip while rocking it from side to side. Reinstalling it is just the reverse.
The idle speed is controlled by what's burned in the PROM; raising it calls for a PROM re-burn. Some resort to using the minimum airflow screw on the throttle body to raise the idle speed, but this isn't the right way to go about it. Using that technique effectively causes the IAC pintel to completely extend, closing off any air it would normally contribute to maintain idle speed.
You'll need a ScanTool or Diacom, etc., to see what the Command Idle Speed is.
Jake
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 3,151
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From: Opelousas, Lousiana
CI 6-7 & 9 Veteran
One thing I have just noticed, the two wire leading to the cold start valve electrical terminal appear to be discolored (burned?) where they come together at the terminal. Could this be the problem?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I would think that a malfunctioning cold start injector would lead to starting problems or if it was adding fuel after start up, you would see or smell the extra fuel in your exhaust. Are there any symptoms to make you think the mixture is too rich?
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 3,151
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From: Opelousas, Lousiana
CI 6-7 & 9 Veteran
Actually, at times it has had some sign of a too rich fuel mix when it was started cold. It sometimes "pops" a little when it is being started, and a few weeks back it was acting like it was "flooding" momentrily when I started it. It has not done this lately, but still does the popping noise sometimes. (Sounds like a minor backfire)
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Originally Posted by crawfish333
I'll try again.
My 88 35th annerversity special (equipped with 4 speed automatic) seems to idle too low (500 RPMs) when at a red light or stop sign after the car has warmed up. This causes the alternator to only put out about 11.5 volts. It does not dies but occasionally will hesitate when I take off. I thought the fuel filter might be bad so I replaced it. This did not solve the problem. The Car runs fantatic when it is not at idle speed. She has only 48K original miles. The car had recieved a minor tuneup @ 43,000 when the distributer cap was replaced and the plugs and wires were checked.
Any ideas?
My 88 35th annerversity special (equipped with 4 speed automatic) seems to idle too low (500 RPMs) when at a red light or stop sign after the car has warmed up. This causes the alternator to only put out about 11.5 volts. It does not dies but occasionally will hesitate when I take off. I thought the fuel filter might be bad so I replaced it. This did not solve the problem. The Car runs fantatic when it is not at idle speed. She has only 48K original miles. The car had recieved a minor tuneup @ 43,000 when the distributer cap was replaced and the plugs and wires were checked.
Any ideas?
If you have a scanner, check the MAF and IAC settingsIf you don't have a scanner, pull the IAC Motor. It should be "clean" and the distance from the front tip of the pintle to the shoulder of the housing(don't count gasket) should be 1 & 1/8 "
Ecm sets the idle throuth the IAC, if it is off, so will idle be
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I don't have a cold start so my experience with it is nil. Usually they get power from the start circuit with ground being provided by a switch that opens when it reaches a certain temperature. The heat is either provided by the coolant or timed circuit from the ECM. Discolored wires, too me, might be indicative of a voltage drop - weak connection at the terminals - which I guess could keep the ground applied a little too long, making it too rich. Someone else with experience probably knows more about it.