1995 P30 ECM Faults (454 TBI)

[1969SSCamaro]

My MH has been constantly idling way too high whether it is hot, cold, etc. I checked the ECM codes and below is what I found:
32 - egr circuit (fuel-injected models); DTC - 32 EGR system failure
36 - MAF sensor error
37 - TCC brake switch circuit error
54 - fuel pump circuit (1986 and later models); DTC - 54 Fuel pump circuit low voltage
71 - A/C evaporator temp sensor circuit error (low temp indicated)

I think (?) all of the code descriptions above are correct as I researched several websites, but still not 100% sure. Regardless,I need to do some maintenance. Could 32 and 36 be related somehow?

Regarding the idle; I read some posts from 2012 where cleaning the IAC valve pintle might be causing the idle problem - could that also cause code 36? I plan to start with cleaning the pintle to see if it helps with the idle and clears some of the ECM codes.

Below are parts I found and trying to decide which ones to purchase and/or in what order;
- EGR Valve ($100)
- EGR Valve Control Switch ($72)
- IAC Valve ($77)
- MAP Sensor ($?)
- Throttle Position Sensor ($48)
- Oil Pressure Sender ($25)
- Switch/Relay; Brake Light ($14)

Any help/experience dealing with these codes would be greatly appreciated. I will also try to test some of the sensors with a digital multimeter, but not sure what I should see. I believe some of the signals would require an oscilloscope to see the sensor output?

Thanks and hope everyone is having a great Memorial Weekend honoring our veterans!

[72westy]

When diagnosing OBD-1 TBI engine always start with the smallest ECM code first in your case 32. Your min idle should be 800rpm (in Park/Neutral) with everything running correctly. The 625 +- is in Drive selection. That is also factory set by GM and the min idle speed screw is covered on the TBI.

From 1995 Chevy manual....

Looking at the 1994 service manual for 454 TBI under fuel systems (Section 4-4A) the 'Min idle speed' setting is... (Factory set screw) not recommended to adjust.

Min idle speed:
For the 7,4L auto trans in Drive (wheels chocked) is 625 (+-25rpm) Closed loop

Controlled Idle Speed is as follows:

Put 454 7.4L in Drive (wheels chocked) 675 (+- 25rpm) IAC count 5-30 (Closed loop) at operating temp 196-222F (add 2 counts for every 1000ft above sea level
The 'controlled idle speed' is obtained by the control module positioning the IAC valve. A high/low coolant temp or AC clutch engagement may signal the control module to change the IAC counts.

IAC counts will be above 60 if idle is too low and zero counts if idle is too high. Things to check if so...
1. Vacuum leak/s
2. System too rich
3. TB obstruction
4. PCV issue
5. AC issue

[jyrostng]

sometimes just tightening up those 3 bolts will fix it. on mine there are 2 gaskets, one cone type and one flat gasket with a steel bead on the exhaust flow side, it's for the exhaust diverter butterfly.

[1969SSCamaro]

Finally got around to working on this and the problem turned out to be the butterfly valve being held slightly open by the cruise control cable; not sure how the cable shrunk. I also removed the IAC and cleaned the pintle (it looked very good) and pintle seat. Also removed the EGR and it looked very good as well. All of the fault codes cleared within a few minutes after starting the engine. It properly idled up cold and then dropped after warming up. It now idles at 800RPM, which I believe is still a little high; spec is 625 +/-25 RPM? I will check for vacuum leaks. I bought a new throttle body gasket just in-case and suspect that is most likely issue. I did pass SMOG yesterday! Also just discovered an exhaust leak; hopefully just a flange gasket. I believe by 1995 GM corrected the "cracking/warping manifold" problems?

[garry1p]

Had the same problem was a bad gasket under the throttle body. Research showed this to be a problem that will throw a lot of codes.

One test is with the engine running spray some WD-40 at the base of the TB and the engine will speed up. That should not happen.



I think it was a $12 fix.

[rgatijnet1]

Also you want to clear the codes and see if they come back or were just a burp and not an actual problem.

[PaulJ2]

Start first by replaceing the coolant temp sensor. Usually located near the thermostat housing area. If it "thinks" the engine is still cold it will keep the idle high. This will keep the other systems from operating normally until the engine is at normal temperature. Inexpensive part to try first.