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.

[marcosv6]

Well, the majority wins. I reverted back to the 60s' and used the old "tube in the ear" trick. Sure enough, the intake manifold gasket is leaking in two spots on the right bank of cylinders. You can actually hear the hissing noise without the rubber tubing but I plan on shoving a tube in the Isuzu service manager's ear so that he will have no doubts. Hopefully that will cure the problem. Only have about 500 miles left on warranty.

Triathlete is correct about the misfiring. At low idle speed a vacuum leak is very noticeable. At higher revs, the amount of air thru the leak is small in relation to the total air intake.

Helps to have a 1970s' British sports car (1971 Marcos). They all leak something! But it's fast!

[johnnyapollo]

I learned the same tube trick tuning a pair of side-draft carbs...

-- John

[marcosv6]

Yep, works better on multiple carb set-ups than any synchronizer I've ever used. I've tuned Webers', Solexs', etc. with the tube. I wonder if it would help with my ex-wife?

Don

[autox-racer]

where on the intake is the leak? at the top split gasket? I found one small leak on the drivers side ground wire on the long intake bolt. There was air sucking past the head of the bolt because the ground wire had a slot in the eyelet. I moved it to the fuel rail bolt and it seems to have helped a lot.

I listened today a little bit with my stehoscope/hose and did not hear a lot of noise. But that was when it was cold. it seems my rough idle is only after warm up.. which leads to vacuum leak.. as things expand and rich warm up goes away. I also used ether and sprayed in the area of the leak and it almost killed the engine.

I changed my plugs to cheap bosch platinums and blocked of the egr with a plate.. no change. other than i have a code now i have to check since engine light came on.

more later.....

[marcosv6]

Fixed! Just got it back from the dealer. New intake manifold gasket installed. No more surging when put in park, and transmission operates smoother (?). Nice smooth idle.

Dealer covered under warranty (has 59782 miles). Thanks for the help.

Don

[Tobert]

Bah humbug. I noticed the hissing this evening in almost the exact same spot. I used the Carb Cleaner/Ether trick to approximate where it is and it's right by the EGR. Tightening the EGR did not help.

Guess I'll try the tube trick and order new gaskets tomorrow :)

Good thread - here are some keywords to help the search engine.

intake gasket leak hissing rough idle surging stall stalling vacuum gas mileage howl whistle