JCF

Hi,

I have a problem with a '98 996 3.4. The car is 80 000 km and runs very good before I made the maintenance.

First of all, I remove the spark plugs (which were BERU models) and put the new ones (which were NGK provided by a car parts supplier). Then I tried to start the car.... and it started. The idle was very bad and the injection indicator light comes on. I stopped the ignition and check the exhaust temperature after some seconds, one was cold. First mistake, I forgot to plug one spark plug.
I plugged back, then I started again to try the car which seemed to run good, in spite of the light was still on....
Then I disconnected the battery and connected it. The car runed good, and the light was off. All was good.

For the next step of the maintenance, I've done the oil draining and filling, oil filter, air filter and the drive belt in the same time, without particular problem.
When the airbox was removed, I switch the igntion on (but not the engine) to check the oil level at the Board Computer. The MAF was obviously also unplugged and I realized after that a new fault code was generated.

After this step, I started the car, and since runs badly. The idle is rough, and the engine seem not to have all its power.
I read the fault code and reset all of them, then check the fault code again, nothing.

I tried to put the old plugs and the idle is better, but there' still a problem.
The sympyoms are the idle, which fluctuate and is rough (and seems to be about stalling), and there is one backfire when I push the throttle pedal quickly to the floor, when the car is at the idle. In spite of them, the car runs nod bad when driving.

I thought about catalysor/lambda probe, MAF (but I've read that it doensn't control during idle), idle throttle potentiometer, idle valve, broken oil filling tube... But everything goes well before, and I don't know why it could fail...

Someone of this forum have an idea of this problem ?

1999Porsche911

Let's start at the beginning. What was the part number of the new plugs?

JCF

New were BKR6EQUP. But I've put the old ones since.

1999Porsche911

You might remove and clean the idle control valve and make sure the throttlebody is clean. Remember, for a few drive cycles after dsconnecting the battery, your engine will not idle smoothly until it relearns your engine's parameters. Additionally, if you are going to use NGK plugs, use the BKR6EK. The one's you got are for the 3.6.

OCNYPORSCHE

I just had a similar problem. Mine was solved because one of the coils was not put on correctly. What was the fault or CEL code?

If it was a specific cylinder, then it is surely that one of the coils needs to be put on again.

JCF

I tried yesterday to remove the control valve and inspect the throttle body.
The valve seems to be good, like the throttle body. When all is plugged, ignition on and engine off, the valve make a noise and is lighty shaking, so I think it works fine.

I also read that we have to drive a few times in order to "stabilize" the injection in the workshop manual, but the battery was already disconnected without any problem.

For the fault code, I don't have a reader here. When checked some days ago, all the codes were results of (big) mistakes I made, and after reseting, any code comed.

I probably will try another code test this week, and check again the coils (but the engine is very good at middle and high speed).

C4CRNA

All hoses are tight all around the throttle body. seated properly?

ejdoherty911

I would start by purchasing new spark plugs. Also purchase the spark plug tube o-rings (two per tube, one inner and one outer). Replace the plugs, replace the o-rings. Make sure the coil packs are not damaged and properly seated on the spark plugs.

I 've had similar issues after replacing spark plugs. I used E3 brand spark plugs (don't). Stick with the proper OEM plugs. One coil pack was not seated properly. One set of 0-rings was bad which allowed oil to foul the spark plug. After getting everything straight, the car ran nice. Improved gas mileage too.

salayc

Check all coils for proper seating and cracks, the coils are commonly cracked when re-torque-ing them. I wouldn't start with o-rings and tubes at this point until you have solved the problem. No sense in adding any more variables.

JCF

How a coil can be not seated properly, when tightened ?
And when you had this kind of problem, the cars doesn't run well at idle, but good at middle and high speed ?

OCNYPORSCHE

Yes, this is what I said too. The coils need to be put back very carefully so they seat on each plug properly. You need to put the coil on squarely on each plug. If there is a slight angle when you put them on, you can easily get a rough idle and misfires.

JCF

Ok thank you, I think I will check again during this week. In your case, did it generate a fault code ?

OCNYPORSCHE

Yes it did, but not immediately. The car worked OK at mid and high speed, but from 2000-3000 RPM I had a problem. Then the idle started to get rough.

ejdoherty911

I would do the O-rings since they only cost a couple of dollars each and with all the time and effort involved with replacing spark plugs spending a couple of extra dollars to keep the oil out seems wise.

JCF

The old plugs were clean, and there isn't any track of oil. The problem appeared as soon as the engine was runned with the new plugs. But I agree with you about the replacement during changing the spark plugs, even I don't remember this o-rings...