Sorry for the post folks if this seems a bit minor, however my 91 camaro has started running very eratically this past week. The engine will run at approx 500 RPM higher than normal constantly (to/from work) at speeds rarely exceeding 45mph. This, in my opinion is fairly dangerous since the car at an idle of 1200 in gear wants to go forward even with my foot heavily on the brake and slowing to a stop requires makes the car shift differently. Also the car has stalled twice off the line (in traffic, so Im not burning the tires). If left alone, the car will start up within 5 min. The 'tone' of the exhaust is even different when this is happening and power seems to deminish. The SES finally came on today for approx 15 seconds and went off leaving an error code of 15 (no other codes were in the computer). What Im asking is two-fold.

a.) will a bad coolant temperature sensor cause this (i.e. is the code 15 really the cause)? I assume that the engine may think it is cold when it isnt, however is this where the engine takes in the reading or is it just for the guage?

b.) after purchasing a coolant temp sensor this afternoon, the electrical fitting is different than the OEM sensor and how should I connect it.

Also could the O2 sensor be causing this? Im gonna replace it anyway, however Id like to figure the idle/rough running issue first.

Thanks for any thoughts on this.

 

The CTS is what is causing your problem yes. If the ECM doesn't know the coolant temp, it cannot go into closed loop. REplacign the CTS should solve most of your problems, make sure to disconnect yoru battery for about 10 minutes after installing the new CTS to let the ECM delete the code. As for the CTS plug beign different, I think they must have given you the wrong one most likely.

 

Some aftermarket CTS units will come with a different plug, however they usually supply a small pigtail adapter to mate with the connectors you have. If not go to another vendor or just get an OE from Chevy. You gave very little information about engine. If it's a fuel injected model you can jump the ALDL connector AFTER it's running and put it in field service mode. If the SES light flashes fast(approx 2-3 times/sec) after the engine is warmed up it is staying in the open loop mode. 1 time/sec you are in closed loop. Code 15 is pretty straightforward, meaning it's not as interdependent as some other codes that can fool you because something else is screwed up. I am not as sure as the other post that all your problems will be solved simply with the CTS. Generally when CTS fails you don't exibit the radical problem you describe. Please supply more about the engine, fuel delivery etc. The ECM looks at colant temp and output from the o2 as well as MAF or MAP inputs to alter engine parameters. Most cases where the CTS input is lost the ECM simply defaults to a predetermined setting. The extremely high idle speed is usually not one of the problems one sees. Check the engine to frame gound, losing it causes all sorts of strange problems.

 

Good point Danno! I had the same problems as him with my 89 L98, there was actaully 3 problmes. I had the same lurching forward when stopped and everything. But my 3 problems were CTS not functioning, a very bad Vac leak, and the EGR solinoid was not functional. But the EGR threw it's own code, so maybe jutt26 just has the CTS and the Vac leak problem.

 

thank you guys very very much for the info. I replaced the CTS this evening with something that Napa gave me (Echlin TS6641). I mentioned to the guy that I had bought the 'status quo' at Advance Parts, however the connections were not correct (Im guessing that they sell the connector separately that I didnt know). The part sold to me wasnt even listed for the car! I took his word at it, being the novice mechanic having only changed termostats, idler arms, alternator and installing a manual electric fan switch in the dash. Anyway, I proceeded to drain half a gallon of antifreeze onto my driveway, and now the code 15 is a hard code (instead of the soft code mentioned earlier). So, after tommorrow when I exchange this CTS with the correct one, NAPA has lost my business. 1.5 hours in NAPA (yes 1 hour standing in line) 1.5 hours replacing the unit because I dropped it into the void between the block and pulleys and the sensor is aluminum so my magnet doesnt work. Some fairly sever burns on my left hand beause even though the car had been sitting for 3.5 hours, I was running out of daylight and the coolant was still very hot. And now the car runs even worse. A lesson in patience is what this is. The positive side of this adventure from my point of view is that I now know that the CTS is the problem (or the majority of it). Also, now that it was replaced (even though it was the wrong sensor, it idled fine for the first couple minutes until it warmed up). Then started stalling to the point where the engine is currently flooded and the battery is on the charger.

To go a bit further, the engine is the 3.1 V6 1991 vin T RS camaro. And of course I have A/c which makes this wonderful sensor kind of interesting to get to with a deep socket 13/16. Also the car has 156000 miles on it, and 3 weeks outta the month will sit at the airport. Ive owned the car for 3-4 years and had the transmission rebuilt last year. I love to 'tinker' on the car, however I do have the luxury of driving my secondary car (7 years old with 49k on it, Jeep). I like driving the camaro alot more than the jeep.

I'll give an update tommorrow night, once the CTS is re-reinstalled with the correct one.

 

sensor is in and ran it for 20 min with no issues...real test will be in rush hour tommorrow.

 

Sound like you have solved your problem but if you need reassurance.

A bad CTS can read erroneous "cold" temps which will enrich your fuel mixture (runs and sounds different) and it will keep your car from going closed loop (bad MPG - runs poorly) and it prevents the TCC from locking up (sounds different - runs poorly - Bad MPG).

So yep a 10 dollar sensor can be a serious demon when it is a CTS and give you stalls, surges, etc. because it thinks your engine is operating at a temp that it is not.

 

worked fine all day. no stalls. back to original idle, and no hesitation off the line.