StudebakerJoe

Help!! My 1999 C5 sputters/misses at idle when hot. No codes on DIC or external code reader. It has new plugs, wires, coils, O2 sensors, and has had the throttle body cleaned as well as the MFS. It has a new PCV valve and hose. I have put some BG 44 in the gas to clean the injectors (still need to run about 1/2 tank). It starts great and gets super mileage. I have also checked the best I can for vacuum leaks and found none using starting fluid. Any ideas? PS. the engine is stock except for a K&N filter.

JR-01

Have you recently oiled the filter?

StudebakerJoe

yes

AnabolicZod

How long does it sputter before it "catches up?" Reason I ask - My 03' does the same thing on a hot start. It will sputter for about 10(ish) seconds, and then run smooth. I'm still trying to figure out why mine is doing this as well. I did notice a decrease in oil pressure during the "sputtering," but as I mentioned, after about 10 seconds, it seems to find it's groove and the oil psi returns to normal. I have a dyno/tune appointment on 04/21, hoping they can figure out what the issue is. Keep me posted if you figure this out, and I'll do the same!

JR-01

There have been some cases when too much oil on the filter has caused problems with the MAF.

StudebakerJoe

I have removed the K&N, cleaned the MAF and installed a Fram CA3914. I will run in garage (it's raining) to see if it's fixed.

StudebakerJoe

It only happens when I am idling at a stop light, etc. No change in oil pressure. My is more like a shutter.

StudebakerJoe

I ran the car until the water temp was around 212 and put in and out of gear trying to simulate the problem. It is much better and will probably improve as the car "relearns" the idle setting. The car came with the K&N already installed. I have had mixed results with K&Ns but none as frustrating as this. I will know more when I get an actual road test. I'll keep you posted.

Thanks

StudebakerJoe

Well, I am back to the drawing board! The road test revealed little change in the problem.

StudebakerJoe

The DIC has no codes. The OBDII has no codes.

Choreo

Only time I ever experienced that was after I oiled my air filter and the excess oil got into the MAF and Throttle body. Really cleaning the MAF and throttle body fixed my problem several years ago.

~Josh

Could be a fuel injector or coil pack issue when heat has an effect. The lower oil pressure is simply because the rpm is dropping.

LT-1s from 92-96 were notorious for optispark issues but another issue that hits almost all of them is fuel injectors after 130k miles.

El original

Had a friend with a misfire issue (not on a Corvette but) could not figure out until a mechanic got a spray bottle with water and sprayed over engine when running. It closed a spark short on a wire that solved/found the problem. Maybe something silly like a wire short, I know you changed them out but hey...Good luck I truly hope it is something as silly as I mentioned. Rob

jjc508520

I had some weird idle problems with my '02 4runner (bouncing idle when cold) replaced the MAF and they are gone....

StudebakerJoe

Update: I decided to check the spark plugs again. I found # 1 plug had two cracks in the porcelain. I don't know how it was broken as #1 plug is not that hard to access. While I was at it I installed NGK TR55s instead of the high priced plugs. I have read that they are a very good plug.
Thanks for all of the help along the way

Modern Musclecar

if you have msd wires throw them in the garbage and buy a set of taylor's or ngk's, if you're using MSD coils go back to stock.