rough idle in park???

[autox-racer]

Hi, my VX just started to idle rough in park over the last week. In gear(under a small load) it idles just fine but as soon as i put in park the idle comes way down to 500rpm or so and shoots up to 1500 and then comes down to normal idle and runs rough.. seems to be missing.

Has anyone had a similar problem? I suppose it could be a small vacuum leak and under load it gets more fuel to smooth it out? Only guessing as it seems some had intake leaks. could it be the intake leaking?

thanks

[Anita]

Anthony,

Discussion here has revolved around the MAS as being a potential cause. To get more info, do a search on (rough) idle.

[Zu4two]

I would think it's a vacuum leak. Or it might be the idle air control valve. Also check the EGR solenoid, both the tube underneath it and it's mounting to the manifold. Are you getting a check engine light?

[marcosv6]

I have the exact same problem. Described perfectly. I just purchased my VX a month ago and the problem existed then. I've cleaned the MAS and even swapped it with the MAS from my 1998 Amigo. No change.

Maybe a transmission valve of some sort?

Don

[VehiX]

I was under the impression that this was either a problem with the MAS or the air intake gasket.

I would check the air intake gasket as you have already swapped out the MAS. Not sure how compatable one would be from a 98 amigo but if it started, ran OK and did not throw a code, it may be safe to say this is not the problem. Check the intake gasket.

[marcosv6]

BTW, the "check engine" light does not come on. I just drove round trip to San Diego (about 20 hours driving) and put injector cleaner in with each tank of gas. No effect whatsoever.

I've also changed the fuel filter, air filter and checked the coil-on-plug connections.

Just noticed I've got 59,382 miles which doesn't leave me much warranty time left. Luckily there is an Isuzu dealer in Ukiah, CA where I work.

Don

[Dallas4u]

Possibly an intake gasket leak.

[Heraclid]

Well I had this same problem and I checked the PCV and it didn't rattle when shook so it was clogged. I replaced it and my idle fluctuation ceased. $3 fix.

[marcosv6]

Forgot to mention I changed the PCV valve also.........no change. Guess I'll check the intake gaskets.

Don

[autox-racer]

thanks, i pulled my pvc and noticed it was not rattling so i cleaned it with brake clean until i made some noise. I will let you guys know if that did the trick... im keeping my fingers crossed.. just seems odd it would only happen in park and not in drive.

[AlaskaVX]

FYI- Some one had this problem when put into drive, no problem while in park. And it turned out to be a manifold gasket.

[Dallas4u]

Sorry, I mean manifold up above... but could be either. May as well check!

[autox-racer]

Well, pvc did not help. So will pull sprak plugs to look for miss fire... maybe help with diagnosis.

Thanks for ideas

[Triathlete]

Usually a missfire will throw the check engine light. At least in my case it did. Plus I would think if it were missfiring it would do so at all RPMs and not just at idle. When mine was missfiring it ran like crap and had no exceleration. I ended up changing plugs (previous owner had cheapo plugs in it) and tapping the fuel rails/injectors. That combo did the trick!

[Heraclid]

Just wanted to clarify - I changed my PCV, air filter, fuel filter, and motor oil/oil filter all within about a two week span. Also ran fuel injector cleaner through the system sometime around then. Changing the PCV was what most most coincided with the idle stabilizing, but it could be that other things helped with it as well.