Idle issues again
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Joined: Jul 2004
Posts: 66
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Idle issues again
I am having the worst time hunting down a gremlin causing a faliure to idle. Actually the car will idle sometimes, but when driving, and letting off on the gas, the rpms just drop off the map. I'm almost certain its the IAC not keeping up. I'm on my second one in less than a year, they are clean, the bore is clean to it. They seem to work good for few weeks, then nothing. I dont have a surge, or stumble. Its just that i have to heel toe the thing just to keep it running. I suspect I may need a new computer(ECM), it think its the signal that is not getting through all the time. I have a '90 coupe, 6speed. Anything else that may be causing this?
Drifting
Joined: Aug 2004
Posts: 1,448
Likes: 1
From: Tracy CA
Have you checked your fuel injectors?
I've got an '89 with an evil bad idle. The IAC was changed with no improvement. The ECM was changed and I gained a little SOP kick, but still wonky idle. I checked my injectors and found 3 in spec (to my knowledge), 4 low, and 1 really low.
Haven't switched them out yet, but I'm hoping this fixes my idle.
I've got an '89 with an evil bad idle. The IAC was changed with no improvement. The ECM was changed and I gained a little SOP kick, but still wonky idle. I checked my injectors and found 3 in spec (to my knowledge), 4 low, and 1 really low.
Haven't switched them out yet, but I'm hoping this fixes my idle.
Drifting
Joined: May 2003
Posts: 1,979
Likes: 48
From: Lakeport CA
You need to check w/ a dealer. The ECM had a silent recall. Mine was replaced around '94 with the exact same problem. After 4 trips to the dealer during which they also claimed, "dirty IAC", they suddenly found that there had been an update. After the replace I've had zero problems w/ that issue.
Now my hunting idle when the speedo is off zero is another issue. I just replace the IAC & the IAC housing, totally cleaned the rest of the throttle body, inside & out with no change. Anytime the care is rolling, forward or reverse, clutch in the idle slowly swings from 800 to about 1100. Once the speedo goes to zero the idle drops to a steady 800 & stays there??
I'm about to call the retired vette engineer & see if he has any ideas. Just saw his number posted here again this last week...
Now my hunting idle when the speedo is off zero is another issue. I just replace the IAC & the IAC housing, totally cleaned the rest of the throttle body, inside & out with no change. Anytime the care is rolling, forward or reverse, clutch in the idle slowly swings from 800 to about 1100. Once the speedo goes to zero the idle drops to a steady 800 & stays there??
I'm about to call the retired vette engineer & see if he has any ideas. Just saw his number posted here again this last week...
Thread Starter
Advanced
Joined: Jul 2004
Posts: 66
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I've got brand new injectors, less than 2k on them. Fuel pressure is right on at 40+. The only sensors that havent been replaced are the MAP and the TPS. I suppose i could have a short somewhere in the wiring to the IAC. Thats gonna be fun to trouble shoot.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Somewhat easy to troubleshoot the circuit, though an intermittent might be more problematic. Since grounding the DLC with ignition on extends the pintle into the throttle bore, do that (typically, you will hear it running). And then with a test light to ground on each IAC harness terminal (disconnected from the IAC), the light should flash. If it's steady, one of the wires may be shorted to voltage. No light is an open on that wire or a bad connection at the ECM.
