CIS Oil Cap Question

DavidI · 03-26-2005, 06:08 AM

I have read volumes of CIS information from my numerous searches and have struck out. My 83SC 3.0 has an intermittent idle problem AFTER warm up. I have searched for a vacuum leak, but have not found one. The idle surges between 1000 and 400, eventually dying after a few minutes. It does not do this all the time though. Here is the confusing part, when I remove the oil cap, the idle smooths out! It should be the opposite from my searches on the BBS.

Any ideas? I am going to continue looking for a vacuum leak. I have read several posts on the dreaded WUR. I may need to make it adjustable like several others have. If it turns out, maybe I can get someone's help so it does not turn into an expensive replacement part.

Thanks, David

bigchillcar · bigchillcar's Garage

i may be way off the mark here, as i'm not as familiar with sc cars..but does your car have an aav? perhaps it is stuck?
ryan

Hladun · 03-26-2005, 06:36 AM

Sounds like you're too rich. When you open the cap added unmetered air leans out the mixture.

Assuming ignition, compression, etc. is OK, the proper way to trouble shoot CIS is:
1. Check pressures with a proper gauge.
2. Set richness with a proper gauge.
3. Then do any other trouble shooting.

bigchillcar · bigchillcar's Garage

david,
did the problem 'suddenly appear' or has it gradually become worse? just thinking that an engine shouldn't suddenly become rich for no good reason..have u recently adjusted the mixture? the reason i mention the aux air valve is that it's specifically supposed to regulate idle..thinking that if it's old and has abruptly become stuck closed, that perhaps this could cause a 'rich idle' condition with fluctuations you've described. wish i had my troubleshooting books handy..
ryan

Gunter · Gunter's Garage

I would check the Auxillary Air Regulator (AAR) and the Auxillary Air Valve (AAV)

fireant911 · 03-26-2005, 08:44 AM

David,
Although I cannot diagnose your problem I can certainly tell you what I did to correct that identical problem on my car... I am assuming here that you are running the car with the Oxygen sensor connected since this is a major part of my solution. What I did was fabricate an electronic switch the uses a normally closed (NC) relay that I spliced in to the Oxygen Sensor wire at the Lambda computer. During normal running I do nothing but after the car warms up sometimes upon restarting the idle is unstable and fluxuates just as you are describing - and at that point I simply flip a switch and the idle is instantaneously steady (it allows the Lambda system to go to open loop mode). After a couple of minutes of driving I simply flip the switch back and everything is fine from that point on (or at least until I stop again and restart). The truly frustrating thing is that this has been extremely hard for me to determine exactly what is causing this due to the randomness of it occurring.

I too have read all the CIS manuals I could get my hands on and this problem was never mentioned. This solution has worked great for me and I even have a brand new, sealed in the box Warm Up Regulator that I do not plan on using yet because at this point my current solution is quite acceptable.

I hope that this help you get things right.

DavidI · 03-26-2005, 11:18 AM

I had the car services at TRE and it ran great about 6 months ago. Tyson adjusted the fuel mixture while it was connected to an emission machine. I have not changed the setting or messed with any of the components.

bigchill, the problem is intermittent and appeared a couple of months ago. It used to only happen once a month. Now it happens every other time the car is started.

I will do some research on the AAV and AAR and try to diagnose it.

Thanks, David

stlrj · 03-26-2005, 12:26 PM

This is sounding more like a frequency valve issue. You might do a search.

Joe