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Good morning
My 1988 Corvette runs poorly at idle which hovers between 600 and 1200, I have a new ECM, MAF, O² sensor, spark plugs, spark plug wires, IAC and such. ALDL gives me codes 33, 42 and 45 I don't know where to give my head. I think these codes are intertwined, where to start?
33 is MAF high. The ecm is seeing a high signal on the MAF.
42 is ESC. Could be the esc module or maybe knock sensor or wiring problem
45 is a rich condition probably caused by the first two.
Thank you for these tips.
I made some measurements: I disconnected the synchronization wire and put the timing light on 6°, I reconnected it and the advance oscillates between +/- 6° and +/- 12° as my idle varies... putting a good blow of gas it gives +/- 32°, no more. These are measurements evaluated with a meter with the engine off and my memory of the position of the mark on the pulley.
I also took readings with Winaldl if it can help things move forward, the first at idle which was at 1000 rpm, the second at 1500 rpm and the third at 2025 rpm stabilized. We can see that something is wrong I couldn't do it while driving because I was alone and it's raining like hell in Belgium.
Oops I made a small mistake the first 2 photos are reversed
Always start with the code set from the front of the engine going backwards, so the MAF code first. There is a code 33 test procedure. If it sees the MAF off, it would definitely cause some running issues. Your IAC counts look fine, so the IAC should not be the problem.
Hello I erased all the codes by disconnecting the battery. I did 1mile with the city and highway car and the codes did not come back, stable idle 1000rpm computer connected normal (10ohms).
When I unplugged the computer, the idle comes and goes between 600rpm and 1100rpm, it's very annoying with an automatic gearbox!
What can I do to remedy this?
Hello I erased all the codes by disconnecting the battery. I did 1mile with the city and highway car and the codes did not come back, stable idle 1000rpm computer connected normal (10ohms).
When I unplugged the computer, the idle comes and goes between 600rpm and 1100rpm, it's very annoying with an automatic gearbox!
What can I do to remedy this?
Then you should have a code being set with the idle hunting. If not, let it run until the code does set, because its got a fault.
You need to follow the Code 33 procedure before you do anything else.
Thank you very much, but for the moment I no longer have a fault code it seems to be intermittent, I will disassemble the MAF connector tomorrow to see what is happening at the pin level and test with my oscilloscope if I I have 30Hz on the green wire in the middle of the connector (terminal c) at idle as I read somewhere
Problem solved a big thank you for your advice and support in my reflections. I measured the signal coming out of the MAF and not 30Hz as I had read but a continuous signal which varies according to the volume of air sucked in full of parasites. The MAF reconnected the engine seemed to give a damn. I reassembled the original MAF and miracle stable idle 800rpm and the car is running very well so far. I had previously replaced it with some crap from Rockauto because there were cracks in the round piece in the middle of the MAF and I had a lot of problems with this car and I did not know how to test it at the time. You taught me new things and took your time to answer me, thank you because in Belgium the Corvette specialists are absent and the parts non-existent.
Code 33, 42 and 45
