Engine Performance problem
1997 Chevy Blazer 6 cyl Four Wheel Drive Automatic 110000 miles
My Blaser will run fine for two days (100 miles worth of driving), then it will cutout when I let off the gas as I'm driving down the road. It immediately picks right back up again but will continue every few seconds. RPM drops off during this time. It will be bad enough to stall when you come to a stop. I had the garage look at it and they couldn't get it to act up, then I stopped in when it was acting up and they quickly put there analyzer on it and they said it was calling for a significant amount of fuel, much more than it should be. They suggested the Coolant temp sensor ( because they thought they saw the temperature fluctuate, I did not see this) or the EGR valve. Here is a list of changes made over the past few months:
- changed coolant sensor
- changed EGR valve
- changed Igintion switch
- changed Fuel Pump & gas tank because of a leak
- changed 3 spark plugs & wires (just haven'y gotten to the other 3)
- changed heater blower (because it failed)
still no help. Again it might go 2 days before acting up then its almost undriveable. Any info would be greatly appreciated.
Check the TPS and the IAC TPS= throttl position sensor, and IAC= Idle air control.
Idle Air Control (IAC) Valve 1. Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" to "B" and "C" to "D". See Fig. 2 . Resistance should be 40-80 ohms. If okay, go to next step. If resistance is not as specified, replace IAC valve. 2. Check resistance between IAC terminals "B" to "C" and "A" to "D". Resistance should be infinite. If resistance is not as specified, replace IAC valve. NOTE: Functional testing of Idle Air Control (IAC) valve requires a bidirectional scan tool capable of cycling PCM/VCM output devices or a special IAC Driver and Noid Light Set (222L or J-37027). Text in TESTS W/CODES - 4.3L article may refer to Tech 1 tester, General Motor's bidirectional scan tool.
THROTTLE POSITION (TP) SENSOR 1. Install jumper wires to enable connection of a DVOM in parallel between TP sensor harness connectors. Connect DVOM positive lead to Dark Blue wire terminal. Connect negative lead to Black wire terminal. See Fig. 1 . 2. Turn ignition on, engine off. Slowly depress accelerator pedal. Signal voltage should gradually change from less than one volt at closed throttle to about 5.0 volts at wide open throttle position. If reading is not as specified, replace TP sensor. 3. TP sensor circuit malfunction should set a related trouble code. For further information, see the TESTS W/CODES - 4.3L article. Also see TP SENSOR ADJUSTMENT in the ADJUSTMENTS - 4.3L article.
Needle should sweep smoothly, no jerking...
November, 19, 2009 AT 4:28 PM
Checked the IAC resistance. 44 ohms between A & B and 45 ohms between C& D, I had infinite resistance between B& C and also A& D. So it checks okay as far as resistance goes. I do not have a Scan Tool to do a functional test. Is there any point of removing the IAC to check for carbon build up or dirt?
I did not have a small enough jumper to check the TP sensor. Will do that this weekend. I also forgot to mention that this whole issue does not give off any error codes.
November, 21, 2009 AT 10:17 AM
Yes, cleaning the IAC by removing it could help, and cleaning the throttle body with throttle body cleaner is also a good idea, some sensors can be slightly out of range and not set a trouble code, these two can do it, so can the MAF at air filter. You can unplug that and go for a ride, PCM will use an average. If that solves the problem, replace it.