sjuhawk2001
New Member
Hi folks!
I'm in desperate need of some help. Over the past few months, I've been working to get my father's 1986 Corvette (L98) back on the road. She's inspected now and running very well with the exception of the idle. When cold and initially started, it'll crank for about 5 seconds or so and fire up. Once started, the car will idle at about 950/1,000 RPMs. As soon as it gets warm, the idles will slowly tick up to about 1,600 RPMs and stay there.
What's odd about this scenario is two-fold. First, it starts and idles exactly where she should for a cold Pennsylvania day but there have been to two occasions now, where she'll idle at 700/750 RPMs in closed loop -- both occurrences were when the outside temperature was below 30 degrees and she had sat for a few days without being run. When this happened, both times, it only lasted for about a minute and the idle shot up to 1,600 RPM again. I feel that, this proves there are no vacuum leaks otherwise, that 700 RPM idle wouldn't be achieveable/possible.
I've done a ton of research and the IAC has been replaced, the TPS voltage is correct @ 0.54 volts, and I even did a smoke test for leaks just to be sure. I've also read a bit about the temp sensor for the ECM being a possibility but I know its working correctly because the fans kick when my cluster read-out is 225 degrees which is sent via a separate temperature sensor.
One final thought... for years, my father always disconnected the battery after driving the car. Could those repeated battery disconnect/re-connects have done something to the ECM? Is an intermittant vacuum leak possibility? Also, wouldn't a vacuum leak cause an idle issue at start-up not when once warm? I feel, but do not know, that a vacuum leak would wreck havoc on the idle at *all* times - not just when warm.
Any help or suggestions is most appreciated. Thank you in advance!
***Note: You may see this cross-posted in other C4 forums as I really want to get to the bottom of this issue***
I'm in desperate need of some help. Over the past few months, I've been working to get my father's 1986 Corvette (L98) back on the road. She's inspected now and running very well with the exception of the idle. When cold and initially started, it'll crank for about 5 seconds or so and fire up. Once started, the car will idle at about 950/1,000 RPMs. As soon as it gets warm, the idles will slowly tick up to about 1,600 RPMs and stay there.
What's odd about this scenario is two-fold. First, it starts and idles exactly where she should for a cold Pennsylvania day but there have been to two occasions now, where she'll idle at 700/750 RPMs in closed loop -- both occurrences were when the outside temperature was below 30 degrees and she had sat for a few days without being run. When this happened, both times, it only lasted for about a minute and the idle shot up to 1,600 RPM again. I feel that, this proves there are no vacuum leaks otherwise, that 700 RPM idle wouldn't be achieveable/possible.
I've done a ton of research and the IAC has been replaced, the TPS voltage is correct @ 0.54 volts, and I even did a smoke test for leaks just to be sure. I've also read a bit about the temp sensor for the ECM being a possibility but I know its working correctly because the fans kick when my cluster read-out is 225 degrees which is sent via a separate temperature sensor.
One final thought... for years, my father always disconnected the battery after driving the car. Could those repeated battery disconnect/re-connects have done something to the ECM? Is an intermittant vacuum leak possibility? Also, wouldn't a vacuum leak cause an idle issue at start-up not when once warm? I feel, but do not know, that a vacuum leak would wreck havoc on the idle at *all* times - not just when warm.
Any help or suggestions is most appreciated. Thank you in advance!
***Note: You may see this cross-posted in other C4 forums as I really want to get to the bottom of this issue***
