Have posted this a couple of times before but havent solved the problem yet.....

-If I drive and take the foot of the gas the idle stays at app.1400 rpm and wont go down until I stop the car, when stopped the idle goes down to 750 rpm.

Scan results
TPS rpm speed IAC
,94 2039 43 120
,54 1942 43 108
,54 1865 43 96
,54 1854 42 81
,54 1800 41 69
,54 1755 41 57
,54 1691 40 47
RPM drops to 1400 and speed to 31, now start braking.
,54 935 18 47
,54 902 11 47
,54 828 5 47
,54 782 0 47
,54 713 0 47

Any ideas....

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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)

 

well...
ill try to see what i can do.
first off im not sure that exports fall into
this catagory, but for emissions purposes
the 'decel' of a vehicle produces a overrich
condition. to remedy the richness the vehicle
speed may decrease, but an artifical high idle
will try to deteriate the raw fuel. hence the
high IAC counts from 1850-1750. as you feel the
engine 'idling' 1400rpm actually the torque
converter is engaged so rotational speed isnt
being transmitted to the rear wheels.
normal IAC counts idle 28-45 is normal. until
the speed is under 30mph the converter then unlocks
and the engine rpm falls equally as speed falls.
ive only seen this occur with a gm correction
with a 2000 c-2500 5.7 vortec. and this was
to cure an idling problem under deceleration.
there really isnt anything wrong. you may see
if your chip tuner may be able to tune some of this out.
hope this didnt muddy the water too much...
airdeano

 

You said if I go under 30 mph the speed will fall.....NOT.....if I start to brake to say about 10 mph and then take the foot of the gas the car will acc. to 1400 rpm and it shifts up too........

More ideas?????

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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)

 

Looking over your data and mods, everything looks perfectly normal. I think most cars will get up to 20-30 mph w/out ever having to touch the gas pedal, although it'll take a good bit more time. The IAC valve follows inputs to the gas pedal some and, as airdeano sort-of said, floats the idle speed some, both for emissions purpose and to keep the engine from stalling out when you come to a stop really quickly. I'm positive the idle speed in your TPIS chip has been raised, and your IAC counts are right on target. Don't forget that the engine still wouln't drop down to idle since the gears/tranny are keeping it revving higher since they're still moving and connected to the engine. At the end of a 1/4-mile run, I'm going through the traps at 4300-4400 rpm and my engine speed is still way above 3k rpm when I let off the gas. It would drop significantly if I shifted into OD, but it sounds better winding down like that. HTH...

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Greg Westphal
'87 IROC 305TPI/A4

 

Hey, i have the same problem except my car once stopped will always drop to 500-550 idle all day long ,unless /and only if you stop and restart the car . then you have to drive and bring car to stop to get correct idle.Need to drive a few blocks not just pull forward. Even coasting after start will cause idle to hold 1300-1500 rpm. Coast till car stops, count 4 seconds and the idle drops and holds till next restart.
I posted in March on this but i'm looking at older posts for clues
Thanks

 

Just a note guys, my idle was going up and down some, tried setting the iac and tps, this helped some, but it was still not right. Tonight I pulled the TB off the plenum so I could pull the iac out and clean it. The screws that hold the bottom plate on (iac screws into it) were loose; I could turn them by hand. The gasket looks like it was leaking too.
After cleaning it all up and putting it back on the car it runs a lot better, the idle is smother than it has ever been.


[This message has been edited by Z_Ghost (edited March 25, 2001).]

 

I can guarentee that I have no leakage on the intake system,(TB,runners,base)IAC is new. Desired Idle is 750 rpm but It wont go down to 750 rpm until I stop the car!

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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 LTR, !plenum, 52 TB, MSD 6AL, TPIS level V prom, Superior shift-kit and all the minor mods, a AFR 195 headed 383 in the works!! ready May 2001...
http://www.itv.se/tacs/members_cars/m279/m279.html (Swedish Trans Am Club)

 

Got the same problem with my '87 LB9/MM5 car, only idle speed hunts way up to 2500 or so.

Braking in gear hardly helps, only thing that restores "normal" idle is blipping the throttle.

I've heard a lot of things, but mostly, that the TB and plenum get "coked and choked", and that taking it down to really clean all the jizz out of there is the place to start.

A dirty IAC can hang up, and throttle plates can stick, too.

Gonna take a swing at it here in a few weeks when the weather gets warm and stays that way.



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Bob
'87 Formula TPI 5-speed

 

Just to let you know, the problem i had with my Z28 was doing the same thing a few weeks ago. I was throwing no codes which was throwing me! Anyhow, it was the tps sensor going bad. Then, my iac was not pluged in all of the way! My tps was at 2.0 closed and should have been .050.

 

My tps goes back to 0,54V, look at the scan results on the first post.

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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 LTR, !plenum, 52 TB, MSD 6AL, TPIS level V prom, Superior shift-kit and all the minor mods, a AFR 195 headed 383 in the works!! ready May 2001...
http://www.itv.se/tacs/members_cars/m279/m279.html (Swedish Trans Am Club)