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Checking the Mass Air Flow Sensor involves looking into the slot on the MAF stalk and seeing if you can observe what looks like a circuit board with components on it. If it looks overall gray, it is covered with soot and needs to be cleaned.
In my case, I used CRS Spray MAF cleaner and it didn't seem to do the trick. Using it in conjunction with a Q-Tip to break the gray soot layer loose of the circuit board did. If the circuit board looks clean with what looks like discrete components on it no cleaning or further cleaning is probably necessary.
If it appears clean and one is still getting related OBD Codes, one is probably better bucking it up and purchasing a new one from Bosch the Porsche OE manufacturing supplier.
Just some thoughts after cleaning a couple of these.
Finally had some time to work on the car again today and not much progress.
I had a stock ECU available to replace the modified s-car-go/Promotive unit I currently have in the car. I thought the modified one had a more rich map. No change in idle behavior.
I also saw the parallel thread about the low battery. I charged mine up as it was a little low. Durametric reported 13.4v at idle. No change in idle behavior.
Reinstalled the old o2 sensors. No change in idle behavior.
I did some O2 voltage measurements over time. One side is about ~.4V pre/post cat. The other side bounces from 0V to .7V pre cat, and about ~0V post cat
Chart below.
I also did some timing measurements over time. As the engine revs up and down the timing also goes up and down between -3 to +10
Chart below.
Durametric only reports DTC code 32 which is an idle problem obviously.
Also took resistance measurements of the ICV in the car vs. a unit I know it works. Both had similar range of resistance between open and close. I also used the durametric to trigger the ICV to open and close it and can hear it when the ignition is on, but engine is off.
At this point I am starting to think there is a hidden vacuum leak as I ruled out the major components of the system that could be potential root cause of this surging idle problem when the engine is warm.
Thoughts?
In regards to questions above here they are:
1. @TheOtherEric Does the car have a RS LWFW- Yes
2. @pp000830@Ed Hughes Did you clean the MAF- Yes with MAF cleaner
3. @IainM Is the clutch original? No- It is a RS one. Needs to be replaced as it is starting to slip. Next on my to do list.
4. @IainM Is the crank sensor bad? I am not sure. It was not in the WSM as an item to investigate. I don't see any DTC codes reported.
5. @mpruden Thanks for the lead on the EVAP testers. I think I will pick one up.
Thanks
Last edited by samurai_k; 08-02-2019 at 04:56 PM.
Reason: Added charts...
Isn't DTC 32 knock sensor #2? On the hammer I would get an Idle Control fault along with an OBD code 0506 (revs lower than expected) and a DTC code of 32.
FWIW I had an idle issue along with 3 OBD/DTC codes including 32. I still have the codes but the idle was resolved by doing idle adaptation. Fully warm the car up, without turning the engine off let the car idle for a full 10 minutes. I was sitting talking to the service writer while doing this and right before 10 minutes the engine stopped hunting revs and went to a smooth idle.
I know you said "The only thing that has changed before the engine started to have problems was new rotors/caps, wires, plugs, and O2 sensors. " but before the idle problem did you clean the engine bay by chance? Also do you know if the RS flywheel was new when installed?
I thought Code 32 was the knock sensor at first, but as I did research and found a factory trouble code document it at actually referenced Code 32 = Idle Air Control. Document below
I believe it is part of a larger document I cannot find as it also has some root cause and solution proposals for each of the codes. Here is an example of the knock sensor problem.
In re to the current RS LWFW that is installed, yes it was installed new by the PO. I need to replace the clutch and inspect and replace any other parts in there.
I was hoping to sort this engine problem before dropping it to do the clutch job. It is a AWD and I don't have a lift so will be dropping the engine and transmission at the same time.
In re to cleaning the engine bay. I did not clean it yet. Its fairly clean with some old oil weaping, etc...
Anyone have the 993 OBD trouble code manual? It is not part of the standard 993 WSM that is widely available...
The reason I suspected (correctly) that you have a LWFW is because there’s a strong correlation between LWFW and surging idle. Happens to me on rare occasions...I get to a stoplight and the engine will surge to maybe 1,500 rpm (?) like 3-4 times then settle down.
Not sure there’s a solution though.
I think you said the vacuum system is ok, and you also did a high pressure test, so I don’t see how you could have a vacuum leak.
I am not convinced yet there is no solution, as the car previously was able to idle.
I just started the car again and for a few minutes was able to do a high idle at 1650RPM then went back to surging the moment I touched the gas.
Need to go back and double check the intake since I did have to loosen the manifold to remove and repair the varioram resonance flap that started all of this!
[QUOTE=TheOtherEric;16014931]The reason I suspected (correctly) that you have a LWFW is because there’s a strong correlation between LWFW and surging idle. Happens to me on rare occasions...I get to a stoplight and the engine will surge to maybe 1,500 rpm (?) like 3-4 times then settle down.
Not sure there’s a solution though.
[QUOTE=samurai_k;16015045]I am not convinced yet there is no solution, as the car previously was able to idle.
The OP's car is a 97, not a 95. Should not have an idle issue with a LWF.
Edited: Clarified what has changed and what is problematic still
Ok getting better!
So I looked at the ICV one more time and noticed the screws on the backside had been drilled out. I pulled it out to compare with my other ICV that I know works. Eyeballing it I could tell the modified ICV had a slightly bigger opening than the working one. I swapped ICV's again and let the car idle for 30 minutes in my driveway. I am sure my neighbors are thrilled with my Fister 3s.
Car is now idling but high at about 1200-1600 RPM. It appears the ECU is going through idle adaption as it will be idling and then start to hunt/surge for a while and then go back to idling.
Idle is still problematic as it will bounce up and down at a stop sign or when I clutch the car and coast the car... but sometimes it will correct itself like @TheOtherEric mentioned. Still not completely drivable on the street yet nor ready for the smog station for inspection yet. Given the ICV is stock and there is a high idle, I am guessing there is still too much air getting in to get the idle down to the 850-900 that is normal.
Not sure which of the changes improved the situation but the stock ECU, old o2 sensors, and un-modified ICV has changed since I first reported the issue.
Last edited by samurai_k; 08-03-2019 at 01:38 PM.
Reason: clarified what has changed and what is problematic
I thought Code 32 was the knock sensor at first, but as I did research and found a factory trouble code document it at actually referenced Code 32 = Idle Air Control. Document below
I believe it is part of a larger document I cannot find as it also has some root cause and solution proposals for each of the codes. Here is an example of the knock sensor problem.
In re to the current RS LWFW that is installed, yes it was installed new by the PO. I need to replace the clutch and inspect and replace any other parts in there.
I was hoping to sort this engine problem before dropping it to do the clutch job. It is a AWD and I don't have a lift so will be dropping the engine and transmission at the same time.
In re to cleaning the engine bay. I did not clean it yet. Its fairly clean with some old oil weaping, etc...
Anyone have the 993 OBD trouble code manual? It is not part of the standard 993 WSM that is widely available...
The manual is Porsche OBD II Manual, WKD-483-420. I will see if I can get one. It's interesting that previous threads have referenced DTC 32 as knock sensor #2 and a local shop said the same thing . Being idle control makes a lot more sense.
I can't comment on the engine behaviour.
However, when discussing the vacuum system: By my experience, vacuum leaks are commonly seen in the rear air intake actuator. The diaphragm fails and leaks. Most components work, but the reduced vacuum at engine revving will make actuators to fail to operate.
A typical problem is a "sagging" resirk flap when you accelerate, causing a whooomphfff-like sound and reduced HVAC air flow.
Cheers,
Tore
Is there a part # handy? And assume you’d swap the soft lines also involved when swapping out, correct ?
I called a Porsche center to get this part, it is listed in PET.
It is really easy to check if there's a leak in the diaphragm, just pull off the vacuum line and suck on the tube going to the actuator.
I am not sure what yo mean by soft lines, I changed the actuator only, not any of the vacuum tubes.
Cheers,
Tore
07-28-2019, 05:23 PM
