Mongo

Cap and rotors have around 30k. The coils are a little over a year old only with less than 6k miles on them. I have heard before, actually John mentioned it in one of my troubleshooting threads a while back that amplifiers at the front of the bay can cause problems. I am still on my originals.

928porschepatrick

This also hapend to me, only at WOT and kickdown. It felt like the engine was going off and on.
All sensors, ignition parts related are new, MAF en LH rebuild
Don't know what caused it. Rebuild my tranny so in a few weeks ill find out if the problem is still there.

Mongo

It's back. Even more noticeable with new plugs. It did not want to idle at the stop light. Idle is also low, around 500. WTF. ISV is still new too!

Mongo

One more thing... Exhaust smell is really rich and yes I have a new O2. It is almost like it is doing the same thing before when I had thatong thread about a possible bad LH. Only thing different now is this skip an bucking while at cruise. WOT is no problem!

WallyP

Check the vacuum lines at the fuel pressure regulator and dampeners for any trace of fuel. Doesn't sound like the problem, but the test is free and easy.

Mongo

Done. No leakage present in the vacuum lines.

Mongo

Just came back from a drive. I still have that bucking at cruise after buttoning everything back up at the rear of the engine. The bucking or surging goes away when you floor the gas, kickdown is smooth and the car has power.

AO

OK. Still sounds like an ignition issue to me. You know all the ignition related components and I'm sure you will diligently work through them to rule each possibility out.

Since you have fresh plugs in there, Now would be the time to pull them and check to see how they look. Is the richness still confined to one ignition bank? Is it all over? You will learn a lot.

But let's assume for a second that it's not an ignition-related issue. The WOT response you get might indicate that it is an overly rich issue and not an ignition issue. So let's think about what could cause this.

1. Bad O2 sensor - I had this once. Actually I still do. I unplugged my O2 sensor a LONG time ago and have been running open loop with great success. We don't have smog checks here in Michigan, so it's not an issue.

2. Bad Temp II - I had this happen to me on a car that I owned briefly. I had the Intake powdercoated and the Temp II couldn't get a good ground. As a result the car would go pig-rich and would not idle well at all to the point of stalling sometimes. As soon as i grounded the body of the sensor, all was well.

3. TPS - Never heard one failing this way (not even sure it's possible), but if the TPS is stuck on WOT, it's going to add a bunch of fuel.

4. Bad MAF - This is pretty unlikely. The MAF seems to be a gradual death, plus they tend to fail the other way (lean). But it's still possible.

5. Bad LH - Again, pretty unlikely, but listing it nonetheless.

Those are the most likely culprits.

Mongo

Will dive into it again tonight. Just a quick FYI, it only happens once and then clears up. i am thinking of disconnecting the battery and clearing up the LH, then work from there.

Bill Ball

You had richness and other running problems a few years ago and I thought we traced it to a bad MAF harness. It sounds now like other parts of the harness may have defects.

Mongo

That definitely crossed my mind too. I cut pretty far down in that harness though and rebuilt the connector. Dunno how much more deeper I should have went. The repair involved cutting off the old connector and the corrosion on the wires where it attached. The leads I attached the connector to were clean I remember. Any sheething that was exposed was covered up with shrink tube. I also taped back up that harness and used flex loom as extra covering of the repair work.

I still find it weird that the bucking and surging along with that erratic idle happened only for a good 30-45 seconds, then cleared up as if there was nothing wrong. Car's idle was glass smooth this morning, but it wasn't fully warmed up.

928porschepatrick

You could check all your ignition wires with an Ohm meter. Mabe there's a bad wire

Mongo

Linking in my old thread before with my MAF harness rebuild. I am starting to doubt the harness could be the issue again. Just completely different symptoms. I ran the car without the airbox just the for ****s of it. It runs fine, unlike before with the MAF and ground issues I had.

https://rennlist.com/forums/928-foru...ge-4-a-12.html

Bill Ball

Right, it's the same but different.

So, are you saying it bucks and surges and idles rough for 30-45 seconds, then clears, then does it once fully warm? Is it also somewhat inconsistent?

I'd be glad to come over and lend another set of eyes to this. PM me with a good day/time.

Mongo

It will have to wait. I am on the hunt for a wedding ring the next few weekends. I greatly appreciate the offer and this time I have a garage for us to do this in as well as a fridge full of beer.

However, yes. I am saying it bucks and surges for 30-45 seconds and clears up while cruising on the freeway at 65-70 mph. It never does it again until you start the car and cruise it on the freeway. If do 80 like I did today, it does not do it! Maybe it can't drive 55. The idle is at 600 now and is somewhat smooth at stop lights (needs motor mounts).