My 95 993 has been idling a bit rough lately and seems to lag in power when shifting from one gear to the other, mostly from gears 3&4. 1st though way my shifting skills however I do believe it might be partially contributed to the engine and something being out of tune. I have only driven the car shy of 3K miles in the last 9 months and the car has 32K total miles. just before I purchased the car, it had it's 30K service. This is my 2nd Porsche so I do have some p-car experience and this rough idle just doesn't seem right and the lag in power isn't always consistent. The rough idle takes place when cold and at operating temperature.

Being that my 1st P-car was an SC (I was able to do almost anything on that car), I am looking for any suggestions (check list)for my 993. Suggestions working from the easiest to the hardest would be appreciated, for this I am lost. I am somewhat mechanically inclined and like to work on my car when I can, however I like to venture into projects like this with some borrowed minds.

I plan to be driving the care more often and would like to resolve the situation on my own before heading to the shop. I have a feeling and hopes it is fairly minor. Thank you.

 

Hi there,

The problem you are describing could be caused by a big variety of problems. If the roughness is only there during idle than I probably (???) would rule out the ignition part. If I were in your position I would however try to get hold of a 9288 tester (Bosch hammer) to check the operation of the various sensors. Otherwise you could try disconnecting the various sensors one by one in order to locate the faulty one.

I hope this is of any help to you

Kostas

 

Rough idle may be caused by a carbon up idle stablizer valve, that's that silver canister object on the top of your intake.

But it does sound like you have other issues too. I would check all the spark plug wire connection making sure that they are in all the way first.

 

Some ideas (roughly in sequence):


- Change the spark plugs (just looking at these might give you an idea of whether its an individual cylinder or something "global"). Was this done at the 30K service or not? Wonder if they screwed something up.

- Throw a can of Chevron Techron in the gas.

- Drive it a couple of hundred miles. 3K miles in 9 months isn't much at all. These cars like to be on the open road.

Robin's got some good fundamental tips also.

 

Sorry, can't give you any specific mechanical advice, but my only comment is I drive my car daily (1995 993 coupe w/ 85K miles), and I've never had any idling or loss of power issues (or any other issues, to that matter).

What I'm trying to say is drive the car and don't be afraid to rev up the engine to redline, assuming engine has been properly warmed up. Like Ray and others mentioned, these cars like to be driven, and I've actually heard of more problems from folks who rarely drive their beauties, than from goof-***** like me who drive 'em daily and take them to the track as often as possible

 

DSN:

Lots of good advice here from the other good folks who contributed!

I would carefully review the work order from the 30K service and see what parts were replaced. I would hope that new plugs were installed.

The majority of these rough idling problems are related to a buildup of carbon at the injector tips, the backs of the intake valves, and the Idle Stabilizer valve that Robin pointed out in the picture. Aside from the latter, these are usually caused by not driving the car enough and too much slow-speed, city driving and prolonged idling.

Like Ray said, pour a large bottle of Techron in there and go drive it HARD for 100 miles or more on the highway. Spend an hour with it at freeway speeds in 5th gear and take it to 6000 RPM when accelerating. This will dissolve the carbon buildup on the injector tips and remove that soft carbon that accumulates on the backs of the valves. This creates lean spots, hesitations, and overall drivability problems as it absorbs the fuel from the injectors. This is a slow insideous process that few people notice until after a fuel treatment restores the lost throttle response and acceleration.

The ISV may be removed and flushed out thoroughly with carburetor or brake cleaner and reinstalled. These get sticky from crankcase fumes and will not bypass the air required for a smooth consistent idle.

Unless there are other issues like plug connectors, igntion wires not seated well in the distributor caps, burnt caps, or oxygen sensor problems, the above procedures should help a great deal. At that point, plugging in the Bosch Hammer and doing a systems scan may display a problem.

Best of luck Sir.

 

DSN, check your dist. caps or better yet, replace the caps and rotors if it was not replaced at 30K service. when my car had its 30K miles services down by the PO P-car dealer, they did not replace it. I don't know if they just skipped it or Porsche did not call for it at 30K service.

George

 

Thank you for all your responses, I will start with the check of wires and fuel additive. Robin, I will also flush out the Idle Control Valve. I actually went to your site last night looking for this as I have seen in your DME section in the past but could not find. Has it been removed? By the way, My RSR Exhaust is awesome, great quality and sound, could not be happierJ


Best regards,
DSN

95 993
99 Lexus GS

 

David,

I never had a chance to do A diy on the idle stablizer cleaning yet. I believe I posted the instruction once long ago.

Basically just take the unit off the car and spray the internal moving parts with a lot of carburator cleaner. Basically the internal cylinder needs to retate freely as you move the idle stablizer valve around with you hand.