Weird idle problem (only when moving)

[gpchris]

After my car gets some speed(about 10mph) it idles at 1500 rpm until I come to a complete stop then it drops back down to 800(ish) rpm. I'm thinking it's PCM related. I'm going to unplug the speed sensor today and see if it's still doing this. Anybody know what it could be?

[RobertISaar]

this the 5 speed 3100 or the 6 speed LQ1?

 

FWIW, with the factory PCM the MC used to change it's mind about idle speed for no apparent reason, sometimes if i threw it in neutral at 55MPH, it would go to ~1000 or less, sometimes it would hover at ~1500, i really don't know what the deal was.

[gpchris]

This is on the 5speed 3.1. It's confusing me so bad because when the speedo reads 0 the car idles fine.

[Addicted To Boost]

After my car gets some speed(about 10mph) it idles at 1500 rpm until I come to a complete stop then it drops back down to 800(ish) rpm. I'm thinking it's PCM related. I'm going to unplug the speed sensor today and see if it's still doing this. Anybody know what it could be?

 

I would say that's normal... my truck does the exact same thing, and has done so since brand new.

[RobertISaar]

hmm.... clutch switch based VSS disconnect? that would do it. not sure if it would trip a code though.

[tornado_735]

FWIW, my Land Rover Discovery does the same thing...it will hold revs up a little bit until I am at a complete and dead stop, and then they will drop to idle. I have no idea why. Doesn't matter if the clutch is in or out.

[GOT2B GM]

my 5 speed z34 does this as well

[Night Fury]

My 91 does too, except its more like 2000 rpm, and it didn't do it before

[White93z34]

my 5 speed z does this. I think its supposed to do it

[mra32]

my motorcycle does it and its carbeurated, but needs a synch badly

[spiderw31]

My Fieros have always behaved like this. I agree, it is likely normal.

[gpchris]

Well it did it before but not this extreme. Any ideas on how I can fix this?

[RobertISaar]

i like the idea of the clutch-switch based VSS disconnect... but that may or may not set a code or do odd things while upshifting.

[gpchris]

Vss disconnect would make my speedo look retarded. I'm thinking it could be like a map sensor problem.. Or tps? Idk couldn't really hear

[BXX]

it's normal and it does that to smothen out transitions when you go back into a gear while moving.

[Night Fury]

it's normal and it does that to smothen out transitions when you go back into a gear while moving.

 

To a point it is, but like he said it got worse, as did mine

[gpchris]

Yeah first 5k miles it idled at 800 and raised to maybe 1200 when in motion which made the brake booster work better and shifting easier but now it's revving pretty high and when I come to a stop sign and don't let it go all the way to zero I don't even have to hit the gas. I just let off the clutch and it kind of jumps. This isn't normal..

[Night Fury]

Same here.

[nelson480]

my car does the same thing, revs to 1500 when started too, idk what thats about

[Night Fury]

my car does the same thing, revs to 1500 when started too, idk what thats about

 

When cold? That IS for sure supposed to happen.

[gpchris]

Mines acting weird now. Like sometimes when you first start it it will run at 2k for like 20 seconds. And when its really cold in the morning it will surge and almost die when coming to a stop. It only does that until it gets warm. As for the original idle problem that seemed to work itself out.

[nelson480]

mine will start at 1100 when dead cold in the morning, the rest of the day when warm it always starts and revs to 1500 like this

http://www.youtube.com/watch?v=f814oEmCc2g

Edited November 6, 2010 by nelson480