Gen2 Engine stumble at 1200 rpm ???

[bhickmott]

Hey Guys .... My Gen2 has developed an irritating engine stumble at 1200 rpm. The idle is perfectly smooth, but as you increse the rpm it first becomes noticable around 1100 rpm. It is worst at 1200 and completely smoothes out 1350. Throttle response is fine and the engine pulls as strong as ever under a load.

It doesn't throw any error codes and I even got the dealer to throw his fancy code analyzer on for a quick check as well. Plugs are new, tried a couple different injector cleaners, cleaned the MAF with recommended cleaner, and cleaned the Throttle Body with special cleaner.

I'd just live it, but when you drive the secondary roads where you spend a lot of time around 40 to 45 mph (exactly in that 1100 to 1300 rpm range in OD) you feel that irritating shake from the engine stumble.

Any ideas ?

 

[kustomizingkid]

I'd bet bum coil... but that 95mm maf might not be helping at all.....

 

[bhickmott]

I would think that a bad coil would more likely show up under heavy load conditions ? If there is a consistent misfire it should throw a code. I can put the car in gear, hold the brake, and keep the rpm right at 1250 resulting in a consistent stumble for as long as I keep it there. No engine codes are produced and you can see the O2 sensors cycle randomly from lean to rich.

 

[kustomizingkid]

100% opposite with COPS... they will run like :q:q:q:q at low loads and smooth out great on the top end...

I had a misfire at the end of the year that made the car stumble between 1500-3000, never even hinted at misfiring at 3000+

BTW it never threw a code... ever...

Go pull out all 8 coils, if the boots are shot start there, all new boots... If that doesn't fix it buy one new coil and switch them out one by one until it goes away...

 

[bhickmott]

What the heck .... the coils are over 10 years old ! I can get a set of 8 Super Coils from Summit for less than $200. I'll just replace them ALL !!!

Thanks for the tip !

 

[nsjuice]

I have the same issues.. replaced the plugs and boots.. idled fine, and the annoying stumble was gone.

Now it's back.. it's the Valve cover gaskets man.. letting that oil into the plugs.. that's my guess.

if you find your coils omit the stumble, please do let us know... in the meantime I'll be replacing my gaskets..

oh.. and when I pull the money magically out of somewhere, I'll do the compressor too.

argh.