gta324

My car idles at 1500 rpm until I stop the car.

IAC is at 47 steps and TPS 0.54 v all the time! Why is my idle at 1500 rpm until I reach 0 mph????

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GTA -89:Free flow muffler,dual 3" HF cats, Edelbrock headers, Vette heads, 1.52 RR 7/16, ZZ-9 cam, Big Mouth, AS&M LTB, ported plenum, 52 TB, MSD 6AL, TPIS level V prom, Mod .MAF, Superior shift-kit and some minor mods. and more to come!
http://www.itv.se/tacs/members_cars/m279/m279.html (Swedish Trans Am Club)

MIKES 88GTA

Did you already adjust the idle screw?
How fast is your setup? how much money in that motor?

kevinc

I've seen similar symptoms on cars not receiving VSS input. Whip out your scantool and observe VSS data.

Basically, the ECM doesn't see the car moving so it thinks you're revving the gas and implements some kind of "anti-backfire" logic to bring the idle down in steps.

-Kevin

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1982 Z-28

See http://www.mycar.net/mafb/registry/detail.cfm?id=276 for details

[This message has been edited by kevinc (edited September 25, 2000).]

84IROC

When you say the IAC is at 47 is this at idle and if so what is the engine speed at idle. The IAC should be no more than 25 at idle(750 rpm 25 counts or less on the IAC). Secondly, I do not understand the TPS statement; do you mean that the TPS reads .54 at idle or at any throttle setting? The TPS should start at .54 at idle and go up to nearly 5 volts at wide open throttle.

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"84Z28/'91 305TPI comp cam flowmaster TB coolant bypass/shutoff valve to heater core MAT relocated Ram-Air(home-made) gutted air-box IROC ground effects/wheels GY245/50's 700R4 superior shift kit/ corvette servo(excellent shift kit BTW) Rebuilt engine and transplanted it myself. Love this engine!
LOW performance people should drive low performance vehicles!

gta324

MIKES....I have no timeslips, and I've put alot of money in it here in Sweden the parts are twice the price comp. to Us.

84IROC....When I drive and take the foot of the gas the car goes down to 1500 rpm, tps drops to 0.54 v and IAC to 47 steps. Then it stays there ( i cant drive slow!!) to make it go below 1500 I have to stop the car, then the idle goes down to 750 rpm (tps 0.54 IAC 47)

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GTA -89:Free flow muffler,dual 3" HF cats, Edelbrock headers, Vette heads, 1.52 RR 7/16, ZZ-9 cam, Big Mouth, AS&M LTB, ported plenum, 52 TB, MSD 6AL, TPIS level V prom, Mod .MAF, Superior shift-kit and some minor mods. and more to come!
http://www.itv.se/tacs/members_cars/m279/m279.html (Swedish Trans Am Club)

petemed

I've got a similar problem but having a T-5 is shows up a bit more. When I push in the clutch the idle will sometimes stay at where it was with the cluth out. If I tap the pedal very lightly then the idle slides back to 750. This would seem like a linkage/binding problem but it's not. My Idle Air is at approx 50 steps and the idle is around 800. If I play with the timing I can affect how the idle works. It's also possible that a vaccum leak would cause the problem - when you are down to 0 mph then the vacuum is lowest. Just a thought.

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1988 IROC-Z
5-speed (was 7R4)
Edelbrock TES

Brian Shaughnessy

The chicken's been doing the same thing.. I haven't gotten around to really investigating it since I'm still breaking it in and still running the old 305 chip for the moment.
If I'm doing stop and go driving, it stays where it's supposed to around 750. However after any length of driving on an open road it'll step down from 1500 to 1200, 1000, then settle around 800/750 when it is finally stopped. Strange... but sounds like not all that uncommon...
As for VSS signals... well, the speedo works and being that it's an electronic speedo and not a cable thing I'm sorta doubting that.
No interference with the throttle body, without the key on it snaps shut just fine.
Just curious if everyone is running without air pump like me and if that might require the engine to be revved slightly to clear out a rich condition upon decdeleration, or if the headers (SLP 1 3/4) might require heated O2 sensor... like I said, I haven't gotten into it - actually this seems to be common, I'd think somebody might have seen it before.


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'89 Formula - Thunderchicken - 355 Vette L98/T-5/3.45 9-bolt/black/t-tops - the fun car!
'90 GTA - The GTA - 5.0 LB9/TH700/3.27 9-bolt/black/t-tops/tan leather - the cruiser.