Warm startup idle woes..

scmguru · 06-04-2009, 02:39 PM

I've got my cold idle sorted out and the car now has a proper cold idle warm up.

However, I seem to have a new problem!

If I let the car sit for 2 hours (65 degrees), it starts immediately and idles horribly for probably 10 minutes.

I now have a low (lean) 500-600RPM idle, complete with popping when I give it gas etc.. on warm startup.

If I turn the a/f screw about 1/8th or so towards rich, it seems to get rid of the popping etc, but the idle is still low.

I've checked and re-checked all of the WUR pressures and have performed a leakdown pressure test which passed just fine.

Hot starts (i.e under 30 minutes) are fine.

System/WUR pressures are as follows

System Pressure: 6.7Bar
Cold Control Pressure at 20 degrees C: 2.1Bar
Warm Control Pressure: 3.75 Bar

Leakdown fuel pressure test:

10 minutes - 2.1Bar
20 minutes- 1.6Bar

I did notice that the WUR control pressure after 2 hours off was higher than the "cold control pressure" (between 2.8-3Bar). Maybe some kind of heat soak?

It's almost like the WUR thinks the engine is warmer than it really is (because the WUR is still warm) and as a result, is causing a lean condition.

Thanks for any insight!

Mike

mark houghton · 06-04-2009, 03:22 PM

Mike and I have been kicking this dog now for some time, and are just about out of ideas. I'm leaning toward WUR problems, but sure would like to hear the collective forum wisdom on this one.

x98boardwell · x98boardwell's Garage

Have you thought about the fuel accumulator. I just had warm start up issues (very lean on warm start for first few minutes and the OK) and it was a defective fuel accumulator. Lot's on this subject if you think this may be your problem.

Best of luck.

Bryan

scmguru · 06-04-2009, 04:56 PM

Bryan,

Tested the accumulator (leak down pressure test) and it passed with flying colors.

One other tidbit, when I cracked open the bottom of the WUR, the bimetal arm was not aligned properly (ie it wasnt parallel with the sides of the WUR like it should be), so I nudged it over a bit and aligned it properly. Maybe something got misaligned (ie spring or pin) when I reassembled

Mark brought up an interesting point earlier. It's almost like the WUR doesn't return from warm to cold pressure properly causing a lean condition on warm start.

x98boardwell · x98boardwell's Garage

When I wanted to test my WUR prior to rebuilding my motor, my buddy had let me borrow his for a day to see if that changed anything and it was all good... and his car ran great so I knew mine was fine. Do you have someone that will let you borrow one for a day? They are very easy to get to... as you already know. This may save you a few $100 bucks.

Bryan

scmguru · 06-04-2009, 06:34 PM

I wish I had access to borrow one.

I'm going to get out the pressure gauge and thermoprobe tomrrow to see where the control pressures are relative to temps.

From what I can tell, there shouldn't be anything that would cause a wur to hang on high pressure and not drop down as it cools.

gogomobil · 06-04-2009, 11:40 PM

My car has the same problem at warm start after sitting for longer than 1/2 hour, starts bad, runs rough (like on 4 or 5 cylinders) for a few seconds and very lean idle after it starts. I am not sure how to test the accumulator but I will replace mine (280€) in a few days. I hope this will solve the problem. Coldstart is just fine.

Btw where is this thing sitting exactly on my 965? I know where the fuel filter is but couldnt see the accumulator without taking the IC off the car.

A930Rocket · 06-05-2009, 12:39 AM

Should be right behind the fuel filter as you look into the engine compartment. It's a medium green color.

Quote:

Btw where is this thing sitting exactly on my 965? I know where the fuel filter is but couldnt see the accumulator without taking the IC off the car.

gogomobil · 06-05-2009, 06:30 AM

Quote:

Originally Posted by A930Rocket

Should be right behind the fuel filter as you look into the engine compartment. It's a medium green color.

Thanks, will have a look in the engine compartment tomorrow

WERK I · WERK I's Garage

Have you tried taking out the Auxiliary Air Valve (AAV) out of the equation during the period of shutdown? I could be your AAV is throwing everything out of wack because it is never closing fully after warmup.
Just plug all the entry and exit ports of the AAV after warmup and try your experiment again.

scmguru · 06-05-2009, 06:42 AM

Dave,

Will try that this morning and let you know.

Mike

scmguru · 06-06-2009, 02:38 PM

No improvement w/ AAV out of the picture..

Same story.. cold start is ok, hot start is ok, warm start boggs at <500 RPM and chuggs to life over about 3-5 minutes.

piscator · 06-07-2009, 09:46 AM

My first post! Great board! I've been lurkin' for about year.

I'm am the curator (

) for our family's 1978 911SC Targa -- 53,000 original miles, owned since new, garaged, this SC is definitely lightly used!

This 911 has the 'warm start problem' and while I'm familiar with 2002, 3 & 5 series BMW, this is the first Porsche I've worked on 'under the shade-tree'.

I changed the accumulator, since this was easy, and got what I'd call a 40% improvement. I wouldn't have guessed that an incremental improvement was possible, but it leads me to ask:

Is there anything about the warm start problem that would result more from lack of use rather than wear? It may be a somewhat 'academic' question, but it's certainly the situation here.

Oil in the Air Cleaner housing? My guess is that this is the result of back-fire on starting or over-cranking, but is there anything about oil in the air cleaner housing that is directly related to the warm start problem?

Thanks for the great insights on this board! It's a nice day here, so now I'll go out an 'tinker'

piscator