My VX idle bounces when rolling in neutral

[djenyc]

An update on my VX idle saga.

This week I was going to swap components from my 92 VX to 94 VX till I figure out what was causing my idle to bounce when rolling in neutral on 94 VX. Just before doing the swap I took 92 VX for a test drive and found that it's actually doing the same thing when I turn AC off!

I then checked 94 Civic VX and it also idles fine with AC on when rolling in neutral. Basically they both have the same condition:

Idle at stop - with A/C ON and OFF - Fine
Idle while rolling in neutral - with A/C ON - Fine
Idle while rolling in neutral - with AC OFF - slowly (5-10 seconds) bounces between 900 and 1200 RPM

So am I on a wild goose chase here?? Should I spend any more time trying to troubleshoot this, or did they just came like this from the factory?

Also both cars idle at around 900 rpm at stop, is this normal?

Thanks
Ross

[djenyc]

Another update - I'm still having the same problem with bouncing idle when rolling in neutral with A/C off.
Now, about a week ago I forgot to turn off my lights and had to jump start the car - while driving with discharged batter I noticed that my idle was steady when rolling in neutral. Weird. It started bouncing again when rolling in neutral after battery got charge. Any ideas?

Thanks
Ross

[Darkelf]

A bit of shot in the dark but have you made sure that all your grounding cables/straps have good, clean connections? I suppose this should also include *all* electrical connections while your at it.

I've use a product called "DeoxIT 5" by Caig Labs. I've found it to be a stellar product.

The testing you've done seems to point to a more systemic issue than a singular component problem (tho you could have vacuum issues on both cars)

Couldn't hurt to go over the electrical connections. Easy and cheap and a good thing to do in any event.

[djenyc]

Darkelf, thanks for your suggestions, may be it's the ground issue, or vacuum, I don't know, probably something I should check out.

I was just taken aback when I found that both my VXes have the same problem - a Canadian model VX 92' with 140K, and US 94' with 260K - what are the chances. And it's such an intermittent and particular problem - only when rolling while in neutral; and as soon as the car stops, they idle fine (and also idles fine all the time when A/C is on) . Since both of my cars do this, I was suspecting that this is a common problem with a common solution. But based on the feedback I received so far that does not seem to be the case.

Thanks
Ross

[XxDrUnKnMuNkxX]

I am also experiencing this problem. The A/C in my VX was removed so i cant test that and I haven't gotten around to replacing my PCV, but i have noticed that while my car is stopped and i pump the brakes the RPMs drop then jump quite a bit. Id like an update on your findings if at all possible.

[suspendedhatch]

900 RPM is too high and what's happening is your ECU is increasing the idle even further when you're above 7mph. Well the combined effect is that it's so high you're actually hitting the deceleration cut off point.

Get it to idle at the factory spec (600 +/- 50 RPM). Could be a vacuum leak from a hose or gasket, timing advanced too far, throttle not closing all the way (dirty, stop screw adjusted improperly, or throttle cable too tight), stuck IACV (take it off and squirt it out with some carb cleaner), or improperly adjusted idle throttle body screw.

Don't forget after any of these repairs you'll need to reset the ECU by pulling the 7.5A fuse under the hood.

[VetteOwner]

ok loping (varying) rpm while coasting in neutral is somewhat normal, gotta remember that the fluid is still spinning around in there and air is still being blasted thru the radiator (cooling it since engine is at idle). could be a number of factors but really as long as it goes back to normal i wouldnt worry unless the loping is severe (to the point of stalling/high reving).

at idle when you press the brakes (hence power brake booster is being used, using alot of the engine vaccumm) it puts a strain on the engine hence makes a different noise. much like when you turn the wheel in a power steering car all the way and try to force it it makes that errrrrrrrrrrrrrrrrrrrrrrrrrrr noise and bogs the engine down.

[djenyc]

VetteOwner, I don't think it's normal - haven't seen this on any other car. It's not too bad, except when I get stuck in stop and go traffic. Also, my idle is a little high, now it's at ~1100 rpm all the time, probably vacuum leak somewhere, haven't had the time to trace it though. Ross

[VetteOwner]

yea 1100 is high, id replace all the vacum lines anyways as im sure thier dryrotted

[Danronian]

I had idle problems with my first VX motor (had 238k on it) and I found it was a sticking throttle body that needed to be lubed and cleaned. I also found the throttle cable was adjusted wrong. To me it sounds like it is either a vacuum leak or the throttle body/throttle cable sticking.