drwhosc

Ok I got a 85.5 NA several months ago, and the car was rough. I knew it would be a project, but the bones seemed to be there. So all of the upper hoses were just shot, and they have been replaced and that fixed a great many idle issues. The car ran like crap when cold, and that looks like it is the thermo II switch. I ordered one, but dropped in the in the 928 because it needed one too, and now the 944 is concerning me so the 928 is becoming my daily driver until I can fix the 944 issues.

I had the timing belt replaced given the general state of the engine. I sent it to a mechanic to save time. Got the car back, it ran OK, but hell of a TB whine, so took the covers off and checked the belts after 100K and tension seemed good. Then one day the car developed two things: A no oil pressure at startup and a hesitation when less than 3,000 rms. I am assurred that the crank bolt has been torqued. I did not check for the green oring.

No oil pressure issue has forced me to limited driving, and I ordered a new oil pressure relief valve. Also probably using thinner oil grades then I should. I got a wix filfer with the anti flowback valve. Hopefully thicker oil and new OPRV will fix things. I checked the AFM and did a clean procedure with a slight bend of the arm to get a new track. Also battling removing a rusted o2 sensor. Going to have to drop the exhaust pipe to get better access for the replacement. Also orering a temp II for the 944.

Here is what baffles me…..
The car runs rough, and I mean rough when cold, but during my no oil pressure time frame which is about 20 secs or so, the idle is perfect. I mean smooth, and spot on. As soon as the oil pressure returns, the rough idle begins and the engine behaves like it lost a cylinder. I checked compression, and all is well and even. I also had oil in the throttle body, so I replaced the AOS seals a couple of days ago, and notice the aos will not hold a vacuum. Got one coming in from ebay since mine is quite brittle. Replacing the seals did not fix either issue. Ok when the engine gets to operating temp, the idle is pretty good. However, when I let off the gas to return to idle, it will drop low around 500 or so run rough a bit, then catch itself and idle near perfect. I think the ISV is working hard though. That also needed replacement.

OK this one is baffling me. I think I still have an air leak. And how does the return of oil pressure, and what I think means crankcase ventilation affect my idle. Am I just barking up a wrong tree here? My initial thoughts were that a temp II sensor would fix the cold idle, and the O2 sensor would fix the hesitation. Could I have some bigger problems? that is why I am up at 2am needing some therapy.

I have a bit of a down time in that I cannot get back to the car until Tuesday, so I wanted to get other thoughts In this mater. Look forward to what others have to say.

V2Rocket

if you need the DME-II temp sensor i think i have 5 or 10 of them (used) laying around...

belt whine is normal but it shouldn't be SO loud...how old are the belts? i hope not 100k...

what tells you there is no oil pressure? do you have an analog pressure gauge or are you relying on the factory gauge? it can be all over the place due to faulty grounds or the oil sender going out. might be a $30 fix instead of a $300.

see if you can find a 22(iirc)mm flare wrench, that will get the O2 off in a hurry.

for the idle, it is likely related to the temp sensor for the DME. the idle speed is controlled by engine temperature. 20 seconds is enough to start to get heat into the block/water and the sensor may not be able to read that correctly.

what do you mean by the AOS not holding a vacuum? while running can you hear/see a leak on the can somewhere? it doesn't see that much vacuum as the suction line to the intake manifold is before the throttle, so any vacuum in the j-boot is caused by the AFM...

drwhosc

Thanks for the sensor offer. They rare relatively inexpensive. the belt whine is getting better, and all the belts are new. Yes I am using the oil pressure gauge on the dash. both gauge and idiot light are lit. Not sure how to proceed here. I will check the sender and make sure it is well.

I did use a flare wrench. Unfortunately it came from Harbor freight, so that might not be the best tool. It looks like the original O2 sensor, and the ends are rounding. I hope dropping the exhaust will help me get that puppy out.

As far as the AOS, I plugged up two the holes and blew are into the third. it would not hold pressure. It was coming out around the top ring.

I just want to make sure I am not missing anything internal. It is just unnerving to see the oil pressure and the rough idle to be related. Thinking about it, I usually do rev up the engine before the symptoms appear, so it is still probably something on the top end. I still have four days to obsess about it.

MAGK944

The drop to 500rpm and return to normal idle when coming off throttle could be the tps. The belt whine is likely your balance belt is too tight, common issue. As to your other issues, sort out the vacuum lines first, vacuum leaks will cause lots of problems that you will spend days trying to diagnose.

drwhosc

Cool so most folks are thinking top end stuff. Hope that is the case.

mytrplseven

I've posted this before regarding vacuum leak detection. You'll hear a few different ways to check and I chose air pressure/soapy water solution. A 2" PVC cap and an air fitting screwed into the cap. Push the cap into the intake of the J boot and clamp it with a "big" hose clamp. Apply 7 to 10 psi to the fitting and spray soapy water solution around the entire engine, under the J boot (hose from t fitting goes to the ISV and other stuff). It's easy to miss this fitting. Also check the cannister next to the battery, throttle body shaft (under the spring), temp sensor under the intake manifold and any other vacuum fitting you can find. Clark's Garage has a good schematic on the routing of vacuum lines. Any leaks will show up as bubbles. Also possible to have leaks on oil filler cap and the AOS unit and hoses fitting to the top of it. Or you could have a mouse in your air filter

Good luck.

xsbank

Wow! I bought a BMW 4 cylinder motorcycle once, thinking it was a fairly hot bike( 100 HP!) and while it ran well and idled nicely, it just didn't seem as fast as I thought it would be. Started routine maintenance and found the same as your photo. Vacuum cleaner and a new filter and away she went! Best performance mod I ever did!

drwhosc

thanks for the advice. it is Tuesday so I can get back to it somewhat. I did this pressure test on the 928, so I have the rig. It was easier to do since i could just hook up to the MAF. I will see how I can get the top end pressurized. Most all the parts came in including a new silicone j boot from Lindsey racing. I hope I get this puppy figured out. I am going to ring the new AOS. it too will not hold a vacuum