Talat

Hello all,

Car was running for about 40 mins on the motorway and then suddenly revs drop. Pulled over to the hard shoulder - car didn't stall and revs cleanly at idle. Try to drive off and again, under load the revs drop until down to idle again. Have it recovered to my Indy but they can't replicate the issue, car seems to be behaving normally.

They are going to get the car hot this time and try again. Anyone seen this before ?

Cheers,

T.

Rocket Rob

My cab did that 2 years ago. I checked the ignition, DME faults, fuel pressure. All were ok. I suspect it was a problem with a lack of fuel because the engine needs more fuel to propel the car than just idling. Unfortunately, I never found the fault. Fortunately, it went away for me and its been running well for a year. Please keep us posted.

Earlydays

Bad DME relay?

Jacke2c

When was the last time that was changed?... maybe partially clogged and isn't flowing... It is a more common problem that you realize...

Talat

Yeah we thought it was fuel pressure issue initially but I think that has been ruled out. I had a sneaky feeling it wouldn't replicate since I managed to drive onto and off the recovery truck ok.

Indy has ruled this out, may ask them replace it anyway as I'm unsure how old the current one is.

Had a major service a few weeks ago and the fuel filter was changed then. The car has done about 150 miles since that service.

Not sure how far to chase this - I'm going aftermarket ECU and ITB's shortly and so quite a few bits on the fuelling side will be changed anyway.

Cheers.

AVI_8

Yes I had exactly the same fault as you described, it happened to me once and I was never able to replicate it. In my case there was very heavy rain with standing water on the road, the only time I drive my car when it's wet is if I get caught out in a shower which is what happened that day so I presumed that water had got into the engine bay and into an electrical connection or HT leads.
I couldn't see any electrical tracking from the plug leads or coil leads.
My DME was reasonably new though that doesn't mean it couldn't have had an intermittent fault. My fuel filter was newish.
Let us know if you find out the cause I'd be interested to hear.
Logan

Talat

Funnily enough it was raining that day, it wasn't particularly heavy though. Last year I drove in much heavier rain for longer and it wasn't an issue. I'll report back my findings when I hear from my Indy.

fiskarflugen

Try cleaning ground near starter. It's right in the path of water spray. Disconnect battery first please.

gchristofi

In addition to ground connections, DME and power connections to ECU under seat, check the AFM connection isn't the cause. There's a few posts on this forum and a TSB for the issue which can cause symptoms you had.

Porsche930

I'm no expert in 964 as my 90 C2 is still new-to-me...does the twin distributor/dizzy belt remained intact?

Goughary

Check the Tsb for the afm plug. That needs to be done, or you will have these symptoms.

If that's been done....I'm going with coils. Complete shot in the dark. But my car did something similar - seems to have been worse than yours in terms of it doing it more often. But coils on their way out were the issue.

Good luck tracking it down.

bmohr

i know others pointed out the DME but I just wanted to add that I didn't think that relay could cause rough running/low or almost no power symptoms..but it can. I always thought the relay just failed entirely, but they can degrade and show strange, seemingly unrelated symptoms such as those above, feeling like running on 5 cylinders, sputtering, etc.

Super90

Just had the AFM plug issue in my car, mainly because I was not careful enough when routing the cable/connector when I put the car back together after a big wrenching session (new plug wires, fan, alternator, caps and rotors, etc.) . That plug had pressure on it from the breather hoses. The car started acting up a few days later. It would hiccup at 3000rpm, then the next day wouldn't idle well and would die at red lights, but then would start right up again. I also noticed when hitting big bumps the car would stumble. That led me to believe it was a connector somewhere.

I rerouted everything and ensured there was proper clearance; all is right again!! Car is running better than ever!!

Talat

Thanks for the comments chaps. Finally had a update and my Indy is fairly certain it's related to the O2 sensor and so they're going to replace that. I'm going to pop down tomorrow and get them to check if the AFM plug TSB has been done and to replace the coils to be on the safe side.

Cheers.