Rough Idle to No Start... Fixed?

[David_B]

I want to thank everyone on the forum, if I have a problem odds are a few other people have had the same problem. So with that in mind I found the search button very useful. However even useless threads are enjoyable with pictures so here is my car. (This was taken at the 2010 Escape in Sunpeaks B.C.)


So I have had my Carrera for a few years now, and she has been mostly problem free. However ever since I started thinking about selling her and moving on problems started showing. I can not afford to have two and I don't want to turn this one into a hot rod I will be looking to buy one already finished. In the end it is so much cheaper that way too.

Okay one of the long standing issues has been sometimes hot or cold the car would crank for what seems like forever before starting. Especially when people are watching. I have been assuming the check valve is letting the fuel pressure drain but since the car never failed to start I have ignored the issue.

All right moving on to the recent issues my Tach started going crazy a couple months ago. Never the same bouncing around sometimes pinned sometimes barley moving at all. Okay that isn't effecting my driving so I ignored it.

Next up the car starts running rough at idle and kinda hesitating on initial acceleration. So I took it home then the next time I started her in the driveway it idled rough and died and never started again.

So at first I thought it was the fuel pump. So I started with running power directly to the fuel pump fuse (circled in red) and the fuel pump fired up.


So next to inspect was the DME Relay, it doesn't matter what I searched when the car doesn't start everyone mentions the relay. So I not only removed the DME Relay but pulled it apart and looked at the solder joints. They looked fine until I zoomed in on the picture, I circled one of the obvious broken solder joints. Compare it to the one directly above and you will see the break.


So I do not have a Soldering gun so I will have to borrow one from a friend. For today I want to figure this all out so how can I by-pass the DME Relay a quick search shows me how to jumper the DME-Relay plug to fire up the fuel pump.


Turn the key and she is alive! Ugh but still running rough... really two problems at the same time?? So I like the quick and free tests, I hate throwing parts at a car. One of the suggestions for a rough running car was the Cylinder Head Temperature sensor a quick and easy by-pass of the the sensor and she is running smooth.


Okay so lesson learned, I will fix the DME Relay and buy a spare. Also I noticed the Tach was operating right which seems weird to me. However until I get the new parts I am not going to start it again. Once I replace the parts I will update my post with the final results.

[Brownie83SC]

Thank you very much for this posting. It has been super helpful. I just bought a 83 911SC and new to the Porsche. Car is in good share and had been checked out/basic service by my local Porsche only shop. Of late been I am having starting problems as well. Starts Greta for a few days then nothing. I find that if I tap the CDC in the engine compartment car starts and runs fine. I am going to take you advice and buy a spare DME and at some point have the CDC replaced. Thanks again.

[David_B]

Ugh, so I am in the middle of a move and trying to deal with that. I was really hoping the CHT sensor would solved my problem, but it didn't.

It took two weeks to get my parts up to Canada, so I left the car alone to deal with my packing. Now my parts are here, so I installed my new CHT sensor and DME relay. Following the advice of other threads on CHT sensor removal made the job easy. Except for trying to get that damned upper rubber grommet in and out. I tried a million tools to grab at it to pull it down but I ended up punching it into the engine bay. Well now it is behind the motor but hey I could reach it, and was able to remove it. Getting the new grommet in was just as hard so I gave up and grabbed some lube and she popped right in.
Okay time to start her up... She is alive! Humm there is a slight stumble when I hit the gas before the RPM jumps up. Not every time but enough to notice. So the car warms up, I drove it down the street all seems fine at first but I turned the car off and made a few checks. I re-started the car and it would barley run, I had to play with the gas to get it about 2000 rpm to keep it running period. So I checked everything I did and it is all fine.

I am not an expert but it kind of smells like it is running rich, so my first thought after reading all these posts on poor running cars to check the Fuel Pressure Regulator, well I am not equipped to do that. Even so people who had this as their issue the symptoms are not a 100% match. So I figured I would start trying to eliminate other possible problems before throwing money at the car. So I have read a few posts on the O2 sensor, so I disconnected it and low and behold she runs again. However with that same stumble on the initial tap of the gas ARGH.

I hope I didn't do this last time I did a valve adjustment but the top two wire part of the plug was broken pulled apart where it should not have.

I did notice while I was running through every check I could do without new parts that I got shocked from my plug wires.
So okay I guess I will add a new Cap and Rotor and wires to my next order (Yay more stickers).

Okay so that makes sense, everything the O2 sensor controls seems to be while the car is at operating temperature. However when I read posts with people with bad O2 sensors it never seemed to run so rough that it would die at idle. So I feel it is something else. I tried running the car at night, and looking for spark but I failed to see anything. However I did hear a clicking that could be a wire arcing elsewhere. I tried killing each cylinder one at a time and noticed a drop in rpm each time.
So my car has 212k Kms (131k Miles) I even thought about re-indexing the wiper arm on the Air Flow Meter some people seem to swear it makes a world of a difference others say it does not.

I am running out of ideas it has been a week and I am ready to open my wallet. Am I missing something? Could this be as simple as a bad plug wire and failing O2 sensor?

[cabmandone]

First let me say, Dude that is one sweet looking car!

Have you checked the Idle air control valve and checked adjustment of the Throttle position sensor. I believe the TPS has a setting for W.O.T and for idle. I can't remember exactly what the settings are but I do recall there being settings from when I was chasing a gremlin.

[steely]

Originally Posted by cabmando

First let me say, Dude that is one sweet looking car!

+1, and

Originally Posted by cabmando

Have you checked the Idle air control valve and checked adjustment of the Throttle position sensor. I believe the TPS has a setting for W.O.T and for idle. I can't remember exactly what the settings are but I do recall there being settings from when I was chasing a gremlin.

+1. I think the WOT is on the right of the Throttle Body and may not be an issue, but the Idle (micro switch) is on the left of the TB - and I agree that and the ICV should be checked. Make sure the idle switch closes in idle and opens when the throttle is opened, and check the ICV for dirt. There are some threads on removing and safely cleaning.

[Drisump]

Hey David, my 3.2 has never had the O2 sensor connected the whole time I've had it. I talked to the senior tech at Weissach and he indicated to me that they're not worth the aggravation. As far as the slight hesitation goes, I find that I need to periodically add some Techron into my tank to deal with this issue... Techron with some spirited driving that is. I'm not sure what fuel you use but I try to use Chevron 94 which is available in some stations in our area. My car is a Euro spec so it seems a little more particular about it's fuel than the N. American spec cars. Cheers