Newbie with a rough running car
 

Well, this is no way to start my posting here, but I need help. Just picked up a 1987 carrera targa, black on black (and yes, I know, pictures will be forthcoming). This is my second P-car (the first was a Cayenne S so it really doesn't count as a P-"car") and I love it already despite the trouble. The car was running rough when I bought it and needed some love. I have changed the O2 sensor, CHT sensor, dizzy cap and rotor, DME relay but the car still bucks and stutters until it eventually dies but fires right back up. It idles ok, but at 1000 rpm. My suspicion is possibly the DME itself or maybe a speed sensor? Anyone in the Cincinnati area willing to test my DME? Would a speed sensor cause these rough running troubles? I don't mind spending a few bucks to get the car running right but throwing parts at it is starting to add up. Thanks in advance.

Kevin

It sounds like fuel starvation, You can check the fuel pressure with a cheapo tool from Harbor Freight or replace the Fuel Filter to see if the symptons clear up.

1000 RPMs is too high. 87 3.2 should be at 880-900 RPMs ( remember the tach starts at 200, 400, 600, 800 then 1000... ) you want to be in between 800-1000 hash mark after she is warmed up.

Just note, when cold for the first 45 seconds your car will be in warm up mode and idle at 1100-1200 RPMs and start a slow decline to 880-900RPMs.

Search for Base Idle adjustement after the fuel filter swap.

BTW, welcome aboard.

+1 on fuel filter, you would be amazed!


81' Widebody SC

As Draco led with: Test before replacing.
- Cheap fuel injection pressure tester and test the pressure at the rails.

- To test DME put the questionable DME in a known good car. If the problem follows the DME then you have an answer. (The reason for not putting a good DME in a questionable car is there are a few failure modes that can damage a DME, such as a short.)

- With the age of the car the rubber hoses are going to be starting to crack. A lot of the real problem causers are on the back of the engine so this is really a pain.

- Check that the intake manifold is torqued to 18 ft/lbs. If there are loose ports obviously tightening will help. ([IBut... ]At the same time the ports that were loose have a higher chance of having cracked intake gaskets...[/I])

http://forums.pelicanparts.com/uploa...1420015063.gif - Always test before tossing money

+2

Welcome Kevin.

Keep us posted on your progress. Lots of smart peeps here. You'll get your car running right.

Thanks for the replies. I forgot to mention that I have done the basic maintenance stuff already. Fuel filter, oil, tranny fluid all changed. I did repair a few questionable vacuum hoses. The bucking, stuttering and stalling "feels" electrical/digital to me. Like a switch on and off. Last night as I waited for the garage door to open, the car was idling fine (albeit at 1000 rpm) and then just died. No warning at all. It started right back up and I pulled her in the garage.

Here's my favorite troubleshooting tool: enter your search term into Google followed by the phrase "site:http://forums.pelicanparts.com/porsche-911-technical-forum/" - I've found it's the best way to find pertinent threads, far better than using the forum search tool. In your case I'd start with "stalling site:http://forums.pelicanparts.com/porsche-911-technical-forum/"

I had a situation similar to yours, but in my case it was caused by the CHT sensor connector not being fully seated, and making intermittent contact.

Be patient and methodical, you'll get this resolved and you'll know a lot more about your car when you're finished.

Good luck!
GK

crank position sensor

Yeah, it does help when we have all the information when we e-diagnos.

It may well be the DME ( ECU ) but before that, let's verify for vacuum leaks.

Normally I do not recommend letting her sit and warm up but in your case. lets do this. Start and warm her up. If she is not going into warm up mode then after 2 minutes, while idling remove the oil cap. Does the idle change?

DME could have a cracked solder joint. Best to get that DME tested in a known good car. I repair a few of these DMEs per month for cracked joints.

But do test Fuel Pressure as well. With car running at idle FP should be 30PSI then remove the vacuum line from the regulator while still at idle and pressure should increase to 35-36PSI.

Also do you have any idea what the mixture is at when idling? It should be at about 14.2AFR or Lambda .98 you need a WideBand O2 for testing your mixture.

Ok. Did the oil cap removal test. It DID make the idle drop a little. I put it on and took it off three times and each time there was noticeable drop in RPM (maybe 200) then seemed to catch it and go back up a little. Other note of interest, as I waited for it to come off 1200 RPM cold start mode, it hiccuped and died. Had to restart, which it did. Someone mentioned crank sensor and I had read on other searches maybe a speed sensor, would these affect the car at standstill?

Speed sensor is the most likely sensor to cause a stall, the ref sensor will not cause a stall. You can actually unplug the ref sensor with car at idle and she'll still run! Try it. If the car is idling and suddenly just dies it's most likely ignition related and not fuel. Test both sensors with ohm meter, they should read 900-1200 ohms. I suggest trying that DME in another known good car.

Tested both sensors. Both test around 930 ohms. But the condition of the wiring near the sensor end is totally degraded.

Any pelicans near Cincy willing to let me try my dme?

If the wires look brittle near the sensor end it's from heat and they should be changed. You can get the BMW sensors for 1/2 the price. Bosch Part #0261210002 and our host sells these.

If you can't find someone to help with your DME you can private message me with your contact info and I'll try to help. I've fixed many of these DMEs over the years.

The other item to check is the ignition switch, I've seen faulty switches cause DME to loose power. With the car at idle reach behind the dash and knock the ignition switch with a screwdriver handle to see if hitting the switch causes problems.

You can also remove the DME relay and jumper these 3 pins together at the harness side connector. Pins 30,87 and 87b can be jumpered together to rule out the relay and/or ignition switch issues. Pins are:
30 - main power from battery
87 - feeds power to the DME
87b - feeds power to the fuel pump
So if you jumper these 3 pins together you feed power to the DME and Fuel pump directly from the battery. Then you can run the car like this just for test purposes to see if the issue clears up. Do this only for simple testing. If this resolves the issue then you know you have a DME relay issue or wiring issue that activates the DME.

Can these test fine, but give problems during actual use? Any tips on getting these things out and replaced? Looks like very tight fit, limited access.

Remove drivers side rear wheel. Then remove the screw holding the sensor, do not remove the bracket that the 2 sensors are in.

But, sometimes the screw for each sensor can be frozen and if this is the case you need to then remove the entire bracket and then on the bench get the sensors out. If you remove the bracket you will need to reset the gap between the sensor and the teeth on the flywheel. Only remove the bracket as a last effort if you can't get the sensors out.

If you find that the screw holding the sensor is frozen try some PB-Blast overnight or better yet mix up some ATF fluid with Acetone 50/50 mix and apply this to the screw overnight.

If the wiring on those sensors looks bad and falling apart replace them, just a matter of time before they leave you on the side of the road with no-start.

Hi Kevin,

I'm north of Cincy (Springboro) but sadly my car is an SC so totally different systems. If you want though, I can take a look/listen at her and see if I have any ideas.


Brian

Ok, small update. Had a 55 degree day here so I got out to the garage for some automotive therapy :) Changed the speed sensor and crank position sensor (black wire covers literally crumbled in my hand). New plugs (this poor car must have not had much maintenance) and now it purrs like a kitten - in the garage. I have not had a chance to take it out on the road yet. But the idle is still high (1000 rpm) and smells rich. I did the jumper wire for the idle adjustment and it settled perfectly to 880 rpm. Is this an indication the ICV is bad? I cleaned it twice, tested the resistance per Bentley (passed) and shook it (makes rattling sound). Should I be looking at fuel trim adjustment? Thanks!

Actually Kevin, it sounds like you did everything correctly and all systems are "go". If it stays warm enough, you might want to take her out for a spirited drive for 20-30 miles...these cars really seem to like it when you drive the piss out of them. Good job!!!