Mart993

Hi there,

1995 993 Carrera, which has started with an idle surge fault that has baffled everyone! After start, the engine runs properly for about two seconds, then surges for about ten seconds, with the idle speed going up to about 1500 rpm, then down to about 500. Try and add throttle is accompanied by pops and bangs through the exhaust and the occasional backfire. Then after about 10 seconds without throttle, the fault clears and the car runs perfectly. When its misfiring the whole car shakes really badly. If you turn the car off, either hot or cold, the engine goes through the same rigmarole

Tried the following, and am now severely out of pocket!

New clutch and Dual Mass flywheel (guaranteed repair!) new plugs (beru) distributor caps, rotor arms, air filter, fuel filter, genuine Porsche drive belts. DME relay, distributor rotor arms both move together. Have checked for vacuum leaks and all seems ok. Its just passed its MOT, and the emissions were well within spec. Engine uses a very small amount of oil but dont think guides are a problem. No independent garage seems to know what else to try, could you help. Sorry dont have a fault code reader.

Love the car, goes superbly when its running right, but my dream car is turning into a nightmare!

Mart993

BobbyT

If you haven't already done it, you may want to clean the idle stabilizer valve. Instructions are here:

http://www.pcarworkshop.com/index.ph...-_ISV_Cleaning

You don't need a fault code reader with the 95 year model. The instructions on how read the codes are long, so I sent them to you as a PM.

RDS928S

Mine will only hunt & surge if very cold. Say below 30 degrees ambient.

NC TRACKRAT

Besides the ISV, this is a WAG, mind you, but I have a feeling you may have trash in the gas tank that's being sucked up every time the car is started, clogging the pick-up.

cpdjfd107

I don't think your post said that you replaced spark plug wires. My car was throwing some misfire codes and engine shaking with a little idle surge (not quite as drastic as yours) and Porsche mechanic (who is one of the best in the US supposedly) showed me a frayed spark plug wire and said replacing wires would fix idle problem. It's in the shop right now, so I can't give you a complete answer just yet.

Mart993

Hi Everyone,

Thank you very much for the replies in such a short space of time.

Haven't replaced the ignition leads, but wouldnt they break down at high engine speeds as well? Thanks for the instructions Bobby T but my car doesnt have a engine check light. Any way I can connect one that you know of. After your replies, went out and started the car, and its almost like the fault comes and goes with almost clockwork precision. Its a warm day in the UK today (for us!!!) about 22 degrees. Its weird!!!

Mart993

MarinS4

Vacuum leaks? Engine temp sensor? What are the codes?

matt777

You've already spent a lot of money on parts that shouldn't have caused these symptoms. I would check out the easy stuff first. The ISV isn't hard to clean. Otherwise I would spend a few bucks on diagnosis at a reputable Porsche shop. My WAG for the cause is the ignition system but that doesn't help much.

ps my Aunt was just out here from the UK (Cheam, Surrey) and I thought she would be happy with our weather. I was surprised to find out that we were having similar weather in the 20's!

J.B.H.

O2 sensors

AOW162435

ISV and or O2 sensor. Good luck.


Andreas

Warpig

Mine will do this when it is near freezing also, but only for the first 20 seconds or so the engine is running.

Nick

Steve Weiner-Rennsport Systems

You didn't say how many miles are on the car, but I would strongly recommend checking the O2 sensor and watching how fast it cycles.

Further, ignition wires and plug connectors don't last 50K so they have more than 30-35K on them, its time for replacement. Old, leaky wires are responsible for a whole myriad of running issues.

Mart993

Hi Everyone,

Thanks for all the suggestions. I am going to clean the ISV at the weekend, but in the meantime I have booked the car in to the local Porsche dealer for a diagnostic tomorrow. I will report back on the findings. There is a bill for new ignition leads 14k ago from the previous owner, (I have owned the car six months) and it has full history and has done 140k miles. Did a round trip of 130 miles today, trouble free, not a single hiccup once the start up shake had gone after both starts! As I have said, weird!!!

Mart993

Timspu

Mart 993,
I have a supercharger fitted to my 993 and she hunts on start up. (Supercharger pulses back through the MAF sensor) The basic idle was a bit low and the Idle stab valve would not operate quick enough to catch it. Ocassionally the engine would cut out when on full lock at idle or approaching a roundabout and throttling off.
I eventually cleaned the Idle stab valve and then adjusted it to give a slightly higher idle rpm. I belive this is a recommend for LWF if the ECU has not been modified. Also i have noticed if i leave the ignition on for 10 seconds or longer beofre cranking the car does not hunt.

Best of luck

Mart993

Hi Everyone,

Busy cleaning the Idle Valve, and checking once again for any leaks. Pipe going to the cooling fan on the left of the engine is badly deformed, so will straighten that out, also the seal for the oil filler pipe is perished and is in the process of being replaced. Readout from the Porsche main dealer is as follows:

42 Fuel pump relay
Intermittent
Present
Short B+

45 Check engine warning light
Intermittent
Present
Short to B+

According to the engineer, everything else checks out ok but he could see a valve hunting backwards and forwards as the idle tried to lock on.

Thanks Timspu (is yours Iris Blue too?) Will give the 10 seconds idea a try when I get it all back together!

Have a good weekend everyone, F1 GP, Moto GP, World Cup and my Birthday tomorrow - could be a classic if supercar behaves itself!!!

Mart993