Hello All,

This is a continuation of a thread on the C3 Engine Forum. 82 Coolant Sensor Replacement. Up to this point I have been chasing a high idle problem with my 1982 CFI. Up to a year and a half ago, I was driving summers with the vette in New England. I pretty much ran the Air Conditioning during this entire time. It was very humid on Cape Cod.

After moving to Arizona, I get to use the vette year round. It does get cool and even cold (32 degrees F) in the desert. But, during the summer and fall it is still very warm here.

I had the intake manifold gasket replaced in order to pass emissions. The car ran well except there was a high idle; 1100 to 1500 rpm with the AC turned off. I also replaced the in tank fuel pump, filter and the short line that had deteriorated. That took care of surging rpm and a bad hesitation on accelerating. The car was barely drivable when it arrived here in AZ. 

So far, I have replaced about 12 feet of vacuum lines, the O2 sensor – due to code, the EGR valve, hooked up the warm air inlet flapper in the intake snorkel, the coolant temperature sensor and today, the MAP sensor. Unrelated but as a consiquince of changing the coolant temp sensor, I had to replace the upper radiator hose which started leaking when I removed and reinstalled it to get to the coolant temperature sensor. My wife wants me to replace the lower hose too before we trek across the desert. I think that is a good idea. That is on tap for this afternoon.

As a note: The EGR valve was installed but was blocked off by a blank of gasket material. The vacuum lines to the air inlet temperature switch in the air cleaner and to the warm air inlet flapper door were missing – had to be done by a previous owner. Many of the vacuum lines were cracked and leaking. I used carb cleaner sprayed lightly around the vacuum lines and connectors to find the leaks. I also checked around the base of the throttle bodies.

I am just getting to the problem of a sheared pivot bolt on the AC compressor lower mounting bracket. Having the lower radiator hose out of the way will help. So the process goes on. I hope to temporally support the compressor while I remove the lower bracket and get the sheared off threaded end of the bolt out of the threaded mounting bracket and replace the bolt. I'll post some pictures of the process. You see, when that bolt broke I had to turn off the AC and the high idle became a real issue. It was idling at 1700 rpm yesterday. The AC loaded the engine enough to make the idle only a little high.

I forgot to ask you before but does the engine go into closed loop?
Rich

Rich, I'm not sure what closed loop is.  I have a 195 degree thermostat. The temp indicator goes up to 200-210 and then just sat there - steady through the 30 minute test drive. I didn't notice any real change after the O2 sensor light comes on.

Now today, I replaced the MAP sensor and the bottom radiator hose which while I had the lower AC compressor bracket out was considerably easier. I got the threaded portion of the broken bolt out of the bracket and put a new bolt in place.  That was very hard to get started until I took the top compressor bolt off and supported by hand.  The bracket came out and went back in pretty easily.  Except for a couple of cuts and a few choice words everything went well.

The test drive was very "better" I think.  I don't have to keep the brakes jacked up going down the back roads and it seems to like a nine hundred rpm idle.  When I let it idle in the middle of the test drive.  I was looking for leaks under the radiator hose.  I heard a couple of clicks and the sound of the AIR pump kicking in. The idle went up a bit and then back to 900 rpm.  I was out side the car at the time. On the way back about 20 minutes into the test drive the O2 code hit again.  No noticeable performance change.

So, yes - better. It was dark by the time I finished so the ambient temp was in the mid 70s.  Nice night. We'll see how it does cold in the morning and it should be near the 90s by the mid afternoon. 
 

Well at least the idle is better..closed loop is when the computer actually will adjust air and fuel ratio on a real time basis..you do need a scanner to see this but is in basic info..well I guess everything is since these cars run on block programs written with if then statements..I will check my old brick system and see if it does anything with the first computer cars..if it does I will have a better idea where to go and why you keep getting the 02 code..are you jumping the ALDL pins 1 &2 and watching the engine light flash or do you have a code puller and what code number is it?
Rich

Rich, I have a reader that plugs into the jack under the ashtray.  It starts by flashing code 12 three times then the code or codes in memory.  The O2 code I have been getting all along is 13.  No other codes have shown up.  I also disconnected the battery to clear the code before running the test drive.  When the O2 sensor came out the business end (in the exhaust flow) did not show black soot. It was a nice brownish like I think we want. The performance is just fine.  Great acceleration, quickness and minimal vibrations now that the compressor is supported and in line with the pulleys.
 

Sounds like mine.  You have changed everything and still high so did I but mine has gotten lower and runs about 700 now. 

I have done the same sprayed cab cleaner around the intake manifold and that is not leaking.  Did you check that also?  It does still sound like a vacuum leak or that you are not going into close loop.

You are in Tucson.  If we were closer, I let you pug my computer into your car and see if it made a difference. 

I balanced my TB's but I do not think that would cause your high idle.  1000 rpm if you do not have any vacuum leaks sounds like it could be an open loop (basically Cold engine idle). 

I believe one way to check to see if you are going into close loop is to start the car and let it warm up if sometime around 185 to 190 degrees the idle comes down you car just went into close loop.  Anyway that is what I unders stand.   Anyone disagree with that?

I found that someone had put in a 165 thermostat in my car and it never got hot enough to go into close loop.  I put a 195 and that and the O2 censor brought mine down to the current idle. 

Just had a thought,  Have you adjusted or checked the voltage on you Throttle Position Sensor?

I'll note how it starts this morning.  I have a 10 hour day at the airport so, I won't get to fool with it too much today.  The drive to the airport is only about 15-20 minutes. Nothing is close out here.

How do I test the TPS? The connectors are very tight fitting.  The TPSs connectors are black with a Green soft surround and a locking key way.  I guess a paper clip or thin wire could slip in while connected or I could make up some jumpers to trouble shoot. I guess that the voltage should start around 5v and go down or start at 0 and go up to about 5v?

Thanks Gilbert and Rich.  I'll post the results how it runs when the outside temp goes up.

Thanks Chip.  I'll check those TPS this coming weekend.  You know I've tried to join that forum a few days ago.  I have not heard back from the forum manager yet.  I am looking forward to reading what they have on the subject. 

Today on cold start everything worked great.  By the time I got to work it was normal operating temps and 900 rpm.  In the afternoon with the AC on in city traffic it was idling at around 600 rpm and the AC worked while sitting at red lights.  So I'm very happy right now.  It wasn't really warm today so, I'll have to reserve further comment until it hits the mid 90s.  I'm sure it will get that warm again before winter.

For now, I'll just be noting anything out of the ordinary and I'll test the TPS this weekend.  I'll also post some pictures.  I have to resize them so they won't take up a lot of space.  Thanks to all for the help.

Are we all good, or what??