FredR

Quite a number of strange things can happen when the LH is in its last legs. My friends S4 would start and run just fine- for about 5 minutes and then conk out. No magic test for this other than replace with a known good one and see if the problem modulates.

In this case there will be a problem testing for this because of the non stock injectors so Ken's chip would have to be supplanted into the test unit thus why good to have a spare LH unit, that or change back to stock injectors for the test [a real PITA].

Rgds

Fred

byrdman454

No problems Fred. My S4 has Porken chips as well. It will be a plug and play. Good thinking to remind him though...Thanks!

auzivision

I had a cough/stumble that went away after having my MAF rebuilt. They tend to fall out of spec eventually. I believe the diagnosis is confirmed by swapping out a know good one. Might be worth a shot.

MAF rebuilt cost < LH rebuild cost.

Don Carter

I had an idle stubble with Ken's chips in my 86.5. I finally figured out that my TPS switch wasn't closing at idle. When I told Ken about this, he said that his chips do require the TPS to be working at idle. After after replacing TPS, idle was perfect.

jerybak

I assume there is a detailed procedure lurking here on RL for checking the TPS function?

Don Carter

You can test the TPS from the plug going to the LH computer near the passenger footwell. I'm not sure if the S4 chips are the same as the S3 chips. You should contact Ken to find out, but it doesn't hurt to check you TPS since it's very simple. They are a common failure.

There's some good info in this Thread

safulop

Fuss with the air filter lately? The air return hose from the bottom of the air box has a habit of coming loose when the air box is shifted around trying to close the lid etc. The main symptom of this hose being disconnected, that I've noticed, is a slight stumble coming off idle.

SeanR

Any air entering before the MAF will have zero effect on running or idling as the air flow is measured at the MAF, under the airbox.

Jason, I replied to your e-mail. Let us know what you found.

Mongo

Yes please let us know.. My 87 does the exact same thing. My S300 chips ARE NOT installed yet. It's not a big stumble but when you get on the gas hard from a stop or revving it at idle.

Jerry, did you ever replace the MAF? I did on mine and it 'helped' the stumble, but did not eliminate it completely. A quick search on here revealed that the next step would be to look at the ignition amplifiers or exciters under a black cover just to the right of the hood latch if you are facing the front of the vehicle.