cant figure this one out

[cam98aro]

when im pulling up to a red light, or to a stop sign, i notice that the rpm's of my engine will hover a little above 1000, then once i come to a complete dead stop, they will drop to about 900 or so

does it with the clutch out in neutral, which really boggles my mind

if this happened in gear, i would think that my input shaft is turning the pilot bearing which is keeping my rpms up until i stop, but it happens in neutral where nothing is connecting my engine to the rear wheels

and ideas i dont recall this happening before i changed my clutch, but i didnt pay much attention either.

thanks guys

[cam98aro]

Re: cant figure this one out

after thinking for a while, im almost positive this is almost some sensor issue, so maybe this thread can be moved, thanks

[hockeyman]

Re: cant figure this one out

Check, clean, or replace your Idle Air Control Valve. They are $31.99 at Autozone, part #AC135 >>for the 98 3.8l f-body's.

The idle on my old 96 3.8 was squirrely for a while until I replaced the IAC. Then it was normal again.

[cam98aro]

Re: cant figure this one out

Check, clean, or replace your Idle Air Control Valve. They are $31.99 at Autozone, part #AC135 >>for the 98 3.8l f-body's.

The idle on my old 96 3.8 was squirrely for a while until I replaced the IAC. Then it was normal again.

thanks, but i do have a question, im not doubting you in any way, but i just dont understand how my rpm's dropping once my car comes to a complete stop would be the effect of the IAC

unless it is somehow getting a reading from my wheel speed sensors or the mph my car is going and is keeping the rpms up in anticipation that im going to start moving again.. because i do notice that when i shift, my rpms will fall and then stop at a specific rpm for a second, which just so happens to be the exact rpm after i let my clutch out in the next gear.. if that makes sense

basically if in in 2nd gear at 2000rpm, then i press my clutch in, it will drop and stay at 1500 rpm for a split second, when i let my clutch out, the rpms dont go up or down, or if i keep my clutch pressed in, they will fall back down again.

[hockeyman]

Re: cant figure this one out

This is what was happening to mine: I would press the clutch & let off of the gas pedal to change gears, then the rpm's would either hover for about 3-5 seconds, or, they would sometimes rev the engine up even higher for about 3-5 seconds. I think I've even hit the 4k marker one time just by depressing the clutch. When I removed the IAC from my engine, it had "major" carbon buildup all over it. I cleaned it, but the problem came back soon after.

You may not need to replace it, just remove it to see if it's dirty or not. May just need a simple cleaning with some mild degreaser and an old toothbrush. Or a current toothbrush from someone you dislike... Your choice.

[cam98aro]

Re: cant figure this one out

This is what was happening to mine: I would press the clutch & let off of the gas pedal to change gears, then the rpm's would either hover for about 3-5 seconds, or, they would sometimes rev the engine up even higher for about 3-5 seconds. I think I've even hit the 4k marker one time just by depressing the clutch. When I removed the IAC from my engine, it had "major" carbon buildup all over it. I cleaned it, but the problem came back soon after.

You may not need to replace it, just remove it to see if it's dirty or not. May just need a simple cleaning with some mild degreaser and an old toothbrush. Or a current toothbrush from someone you dislike... Your choice.

im pretty sure i have had it out before, i remember pressing on something, and my car wouldnt start after i did that.. pretty sure it was the IAC

i find it interesting you said that, because once in a blue moon my car will rev up after i press the clutch in and let off the gas, every time it happens i think im going crazy and forgetting to let go of the gas, but it stops after a few times

[nascar24jd]

Re: cant figure this one out

So, did you ever solve the problem? I seem to have the same one...

[loser]

Re: cant figure this one out

im pretty sure i have had it out before, i remember pressing on something, and my car wouldnt start after i did that.. pretty sure it was the IAC

i find it interesting you said that, because once in a blue moon my car will rev up after i press the clutch in and let off the gas, every time it happens i think im going crazy and forgetting to let go of the gas, but it stops after a few times

my car does this too, backing out of my drive way, ill put it in reverse, let the clutch out anough to "coast" me back and ill toss it into nuetral and roll back and the rpms will rev a tad when i do this too, just like you said. but think about whats happening, im letting the clutch grab a little, then putting it back to the floor, theres a load on the motor for that split second, so obviously if you remove that load ( nuetral ) the motor is going to rev up a tad.

personally, i think your nuts. i dont think anything is wrong, stop worrying.

[cam98aro]

Re: cant figure this one out

So, did you ever solve the problem? I seem to have the same one...

which problem? the car staying at idle until i come to a complete stop, or the other problem with the reving up?

i would replace the IAC, but $35 is a little steep to fix a "problem" that isnt really effecting anything, if you know what i mean.

my car does this too, backing out of my drive way, ill put it in reverse, let the clutch out anough to "coast" me back and ill toss it into nuetral and roll back and the rpms will rev a tad when i do this too, just like you said. but think about whats happening, im letting the clutch grab a little, then putting it back to the floor, theres a load on the motor for that split second, so obviously if you remove that load ( nuetral ) the motor is going to rev up a tad.

personally, i think your nuts. i dont think anything is wrong, stop worrying.

yes, but when mine does that, it will rev up to 4500 and stay there for around 3 seconds, thats not normal at all, i know that is the likely cause of the IAC. and this is at shifts of around 2500rpm.. but im not too worried about it because it happens maybe once a month.. if that.

[nascar24jd]

Re: cant figure this one out

My car is doing something similiar. I have 2 spare IAC units and I have tried all of them with the same results. My car idles at 1800 rpm when in motion, and about 3 seconds after coming to a full stop it settles back down to an idle of about 900 rpm.

I have an automatic transmission. I do not think it is the IAC. I really think it is somehow related to the vehicle speed and/or the VSS. If not, then the ECM/PCM must be sending the wrong information (voltage) to the IAC. I am at a loss at this point...

[RadRacer]

Re: cant figure this one out

My car's kinda the opposite; if I push in the clutch and just coast, the idle drops down to about 800 or so, but comes back upto 1000 once I near a full stop.

[nascar24jd]

Re: cant figure this one out

I don't mean to highjack this thread, but maybe we can all help eachother out.

I just tested the IAC with my ohm meter and it checks out fine according to the Haynes and Chiltons manuals. It is installed properly and the passages are clean.

I am really thinking that I have a PCM problem. I am going to check ebay and the local u-pull-it to see if I can grab one for cheap.

Maybe it works, maybe it doesn't. Right now I got the car to an idle at 900 rpm and I unplugged the IAC. It is really the only safe way to drive it.

Driving it the other way is very dangerous. When I try to stop the car it wants to keep going since the engine is revving up at 1800 rpm.

[cam98aro]

Re: cant figure this one out

My car's kinda the opposite; if I push in the clutch and just coast, the idle drops down to about 800 or so, but comes back upto 1000 once I near a full stop.

mine does this when my injectors are shut off when im not on the gas, just engine braking, but when im driving normally it does what i described.

[cam98aro]

Re: cant figure this one out

My car is doing something similiar. I have 2 spare IAC units and I have tried all of them with the same results. My car idles at 1800 rpm when in motion, and about 3 seconds after coming to a full stop it settles back down to an idle of about 900 rpm.

I have an automatic transmission. I do not think it is the IAC. I really think it is somehow related to the vehicle speed and/or the VSS. If not, then the ECM/PCM must be sending the wrong information (voltage) to the IAC. I am at a loss at this point...

well, tell me if you ever get it fixed.

i cant really help you on this one, because i have never driven an automatic car that had a tach, so i dont know what they are suppose to do

[nascar24jd]

Re: cant figure this one out

Thanks, and you do the same. Sooner or later one of us will figure this out.