Hello All. Here is the Problem. The Car has developed a problem where it stumbles a bit on cold start up then runs fine for about 15 minutes and then starts to rev up to about 1250 - 1500 and shows no ses light. Otherwise it seems to run fine (allthough hard on the brakes and tranny!!). I have changed IAC(and reset it), changed TPS, O2 sensor, and cleaned the throttle body bore and plates. I have tried to find vacum leaks with a can of carb cleaner but cannot find any (or maybe i'm not searching well enough.. any usuall bad spots i may be missing??). I have tried unplugging the temp sensor but still the same thing. Another symptom allthough i'm not sure its related is the gas tank seems to be accumulating abnormal amounts of internal pressure (a lot of gas fumes hiss out when releasing gas cap). This is all quite strange to me as i'm used to the vintage muscle cars. The car in question is a 1990 GTA 5L Auto bone stock. I am completely stumped guys... can some good soul out there please help me keep this faithfull old warrior on the street. regards...

 

Welcome to TGO!

PCV, EGR, and brake booster. Get them? A bad injector O-ring can also bleed some air past. is the throttle shutting completly? Perhaps the throttle shaft is worn?

 

Thanks Stekman. I'm somehow doubting that there is a vacum problem. The reason for this is that when it idles way up to 1500 (or even higher now!!!) i can hear the hissing of the IAC valve open wide. Eventually the car will get sick of this high idle (for lack of better words)?? and it will go back down to normal for no obvious reason?? (the IAC closes and everything becomes OK). Can the temp sensor (fron of block) possibly be the culprit.

regards, continually stumped.

 

Well, I think that narrows it down to the CTS. If you pulled the connector from the T-stat, you pulled the one that the gauge uses. The CTS that is in question is the one that the ECM uses for fuel determination. This is located in the passenger side cylinder head, located between #6 and #8 cylinders.

Can you check resistance? Get a known temp reading and cross reference with the ohms (chart courtesy of Vader)

 

Hey Thanks Stekman. I will check out that sensor ASAP and post what i found. I appreciate the time.

regards

 

Hello again. I took a look at the sensor on the passenger cylinder head (one wire exiting) and it appears to have a far too high resistance. But now i'm confused. The sensor i unplugged earlier this week at the front of the intake manifold with two wires (i think yellow and black) did not effect my temp guage at all.. in fact Haynes says that is the temp sensor that has the effect on the ecm and the fuel injection system. Furtheremore when i unplug both of these sensors and run the car, it's temp guage works, the fan turns on (or at least one of them does, the other is activated with the ac), and the car runs ok.... so far??? Damn i'm confused now. I may have to resurect the old 68 charger rt as a daily driver now. I'll keep any results i find posted. Could haynes be wrong?

regards..

 

Nope, I think I got my sensors backwards

Fan switch is the single wire connector in the head between the 6 and 8 holes. When the temp gets hot enough, it turns on the fan.

The one on the intake then is the ECM (if it has 2 wires coming off of it)

Sorry about that, brain cramp.

When you say "both of these sensors" do you mean the fan switch and the intake temp sensor?

 

While we are on this topic, where can I trace the wire for the temp sensor between #6 and #8 sensor. Long story, but this shop messed up my wiring really bad and I can't find it. So none of my coolant sensors are hooked up and my car idles funny.