Minor problem solved
 

I wanted to share a minor problem that I have been having just in case anyone else has this also.

My car (84 911) has been had a minor bounce at idle for a little while and it was a little low (around 750 RPM).

I had been thinking this was because of a vacuum leak but I searched high and low and can not find one

I decided to order a new CHT sensor and o2 sensor from our host just because the where both very old and thought it be good to upgrade (old CHT sensor was single wire type).

I performed the upgrade the other day and I took my car out for a nice hard ride today after damn Irene left us, my idle is now where it should be bout 850 RPM and it feels like a different car. I also felt like my car was running a little rich before and dont feel that now.

I cant tell you if the fix was the CHT or o2 sensor (I think probly o2) but if you have single wire CHT you should do upgrade (was very simple replacement) and if your o2 is old (I believe every 30k miles is recommended) it should be replaced.




Hope this helps someone with same annoying problem I was having

Cool. I had a similar experience with my SC.

The O2 system on my 81 has a relay next to the CIS brain under the passenger seat. It is square not round like the ones in the front trunk. A guy was saying his car ran better just by replacing this relay even though it was not bad. I did it for fun and it really made a difference. Crisper feeling. Not faster - just better response. Like a tune up.

I was thinking that maybe your temps dropped so much that the colder air made the car run better - but it's 70 degrees in Bel Air after 10PM.

Sorry to rain on your parade but is your car chipped? If so then you are good to go at 880RPMs if not OEM chip must be 780RPMs

Check at Base Idle via the Jumpered B & C per bentley.

It is probably the the new O2S which modulates the idle via the ICV.

Jim

My car has OEM chip right now, It was idling at the 2nd hash mark below 1k RPM and when I would stop at a red light it would kind of bounce up and down just a little bit, this was just a little annoying to me.
Now it idles steady right between 1K and 1st hash mark below, also the car does feel a little crisper

I think I'm up for a preventative changeout of my O2 sensor.....

Best!

Doyle

Oh I see.

Remember our tach starts at 200, 400, 600, 800 then 1K

So in between hash and 1K would make it 900RPMs.

About 1-2MM below the hash below 1K is where the OEM RPMs should be at 780RPMs.

I agree at 900 RPMs our OEM idle for 84-86 feels better but it will over work your ICV via the DME. The ECU will constantly want to go to spec 780RPMs but you overrided it by a manual adjustment. I think the AFR will be thrown off too.

I would remove, clean with carb cleaner until clear and spray some silicon based lube in the ICV. Also check the OHMs. In fact. re-adjust to 780RPMs and when she bounces leave the car on pop the lid and tap on the ICV, if she clears up, you found the culprit.

Just my 2 cents, if you happy then so be it :D

Jim

Jim what should the OHM reading be on the ICV?

Let me check the Bentley. BRB

Between the two outer terminals 40 OHMs

Center and either outer terminals 20 OHMs.

thanks Jim Ill go check it now

I show 44 outer and 22 center to outer..so that looks good....I think I will remove it tomorrow and give a good cleaning

by the way i replaced CHT for two reasons, 1st for the upgrade and because it was only reading .3 ohms (should be bout 2ohms)

Strange but maybe OK, your DVM seems to be reading 10% positive. If your DVM is accurate, then 10% positive resistance may or may not be acceptable. Hmmm.

Yeah, try the thorough cleaning. Use a non residue carb cleaner and be generous with the cleaner until you see it come out clear.

Find some silicon based lube and just quickly shoot the lube and rattle the ICV to work in the lube. Dry off and replace, also clean the contacts.

Drive her around until hot then set your base idle to OEM spec.


Using a piece of 10 Gauge wire, jump B & C terminals in the engine bay at what appears to be a round relay empty socket and set the base idle to 780 RPMs then see if the hunting re-appears.

Jim