Warmup idle issue
 

I'm still trying to get my Carrera idling properly. It now idles fine when cold and then when the oil temperature reaches 180 degrees. It's just lumpy during that in between period. The head temp and 02 sensors are both new. Intake manifold gaskets are new, injectors were checked and everything was recently tuned. The CO is correctly set at .06. Off idle it runs great, no matter what the engine temperature is.

Should the idle be smooth throughout the warm up period or is this just typical Carrera behavior?

Thanks.

bump.

Can't tell you what a Carrera should idle like (I have a CIS system). A friend of mine has a 78 Jaguar that has the DME system. He was getting stalling during warm-up as the system would go too rich. He changed the regular culprits but still couldn't get it to work. The DME system uses what can be described as an analog computer so it drifts with age. What we did was put a 15K ohm variable resistor in parallel with the temp sensor ( the head sensor on a Porsche) this makes the computer think the engine is warmer than it is and you can adjust the resistor to get a smooth warm-up. His stalling stopped completely. When the engine is warm the head sensor has a low resistance (couple hundred ohms) so the parallel resistor has no appreciable effect. The Jag system can adjust richness so you can properly reset the CO for a warm engine taking into account the parallel resistor.

Mixture? (Sometimes the simplest solutions are the best.)

The mixture was adjusted to within the factory CO spec but I'll try richening it a bit to see if helps. Thanks.

It turns out that the mixture screw was 1/2 a turn from fully closed. Turning it in all the way made the idle a bit better. That would seem to indicate a vacuum leak somewhere, but I sprayed carb cleaner with the 02 sensor and idle stabilizer valve disconnected and the idle stayed steady. I also noticed that the car runs better with the new 02 sensor disconnected. Any thoughts?

JP,

Do a search. There has been lots of discussion on O2 sensors.

I don't have an 87, but I do have an 80 engine w/CIS and it sounds like you have richened up the mixture an awful lot. The general consensus seems to be that one complete revolution of the screw is about 8%CO.

Why not get back to Steve /Wong and see what he says?

I spoke with Steve yesterday and he thinks there's a vacuum leak somewhere and the car is running too lean at idle. He can make a chip with a modified (richer) idle mixture but that would be only a band-aid solution. I will only go this route as a last resort. Also, the idle and drivablilty is worse with the stock chip reinstalled (in case anybody out there was wondering ;-). )

Alternatively, he could supply a chip designed for an open loop (no 02 sensor) system. I am running a european premuffler, so the cat is of no concern. Has anybody gone this route?

John and I did just talk about it. Car was running absolutely fine prior to the recent top end rebuild after finding a broken head stud. Seems this all happened after the rebuild after so I suspected a vacuum leak somewhere, - the setting of the afm screw and CO readings are pretty lean. Then there was also the incident after the rebuild where the mechanic initially mistimed the cams and startup rusulted in a nasty clashing noise, so it was shut right down. Cams were reset and subsequent leaddown measure in fine at 5-6%. I supect something very simple that got altered upon reassembly.

You did mention replacing the fuel pressure regulator with a new one from Pelican for $30!?! It should be 2.5 bar with the vacuum line disconnected, so you may want to check that it does not measure below this. Even a 0.25 bar reduction will result in going too lean. Also, check for possible corrosion or poor connection on the O2 sensor connectors which could cause a erratic feedback signal.

Steve,

The pressure regulator should be correct, as it had the same part number of the one it replaced. I can't recall the actual price but it was alot cheaper than $60. A mistake in the Pelican parts database, maybe?

I haven't had a chance to check the fuel pressure, since I need to find an adaptor between my gauge and the port. Any idea what the thread type and size is for this port?

Thanks.

If the numbers are the same on the new regulator, then I would think it is perfectly fine. Looking at my manual, if you ever want to measure the pressure, the test port is a compression fitting with M 14 x 1.5 threads. Watch for the sealing ball inside the cap.