I have a 1986 Corvette Coupe with the L98 and 700R4. I'm chasing what appears to be a MAF-related issue and I'm looking for advice from anyone familiar with the early GM MAF systems.

The car sat for approximately five years before I bought it. Since getting it running, I've installed a new Delphi MAF sensor, installed a new IAC valve, tested the MAF relay, performed battery resets, and checked for possible vacuum leaks around the intake system. Timing has been verified and set correctly with the EST bypass disconnected.

The issue is that the engine does not idle properly with the MAF connected. It will start, but the idle hunts, drops RPM, and often acts as though it wants to stall. If I hold the throttle around 1,000 RPM for a short period and then slowly release it, the engine may catch itself, but it still does not idle normally, and eventually loses idle and dies.

However, if I unplug the MAF while the engine is running, the idle immediately stabilizes and settles at approximately 600 RPM. The engine then runs smoothly and consistently. At the moment there are no active trouble codes while the MAF is connected.

The car does have an exhaust leak at the EGR tube where it connects to the exhaust manifold, which i need to find a clamp for, but otherwise it runs and drives well.

Based on these symptoms, would you be looking more closely at the MAF sensor itself, the burn-off circuit, the wiring between the MAF and ECM, ECM grounds, or something else? Any recommended voltage checks, pin tests, or diagnostic procedures would be appreciated.

 

Were the injectors cleaned and flowed ?

 

They have not been, but i did a top end teardown and they were in good shape, the engine is surprisingly smooth when the MAF isnt plugged in.
i did some testing while it was plugged in, was able to get it to fire up and hold idle for about 30 seconds while i poked around with a multi

The only wire im concerned with is the signal wire, when unplugged it gives a 5.0v reading which should be correct for this car, but when plugged in and idling it shows 1.5~ with light revs making it increase to around 1.8
im pretty sure it should be at 3.5 at idle, this is a brand new MAF and i just cleaned it before testing today, its hard to do extended testing with it plugged in due to subsequent testing making it hard for the car to even start with the MAF plugged in, i need to unplug it, drive it around, wait for it to cool down, then start for more testing every time.

considering the voltages i got could this MAF just be calibrated incorrectly? its a Delphi AF10320

 

^ also the engine has 50k miles so i dont think the injectors have any issues

 

Engine mileage has nothing to do with condition of injectors.
what is maf gps at idle ?

 

I don't currently have a way to read MAF grams/second. I was measuring the MAF signal voltage directly and saw approximately 1.5V at idle with the MAF connected and the engine running poorly.

 

23gps or close to that if that’s correct, way to high if that’s correct. Should be closer to 6gps. Have you smoked tested the intake ?

I would think ecm feedback would be .40-50 at idle

 

The 23 g/s value came from a scan tool? I don't currently have a way to read live MAF data, gonna look into getting one, im near confident there are no leaks but ill also grab a smoke machine to test

 

Just looking at the binary tune is how I came up with the voltage vs gps
otc pathfinder, mr2500 or moates has a xtreme aldl cable that works well with winaldl.

 

Ive got a ALDL cable on the way, ill report all the information i can once it arrives, thank you for the help!

 

86 can be hard to connect to but winaldl should work to see tps and maf gps. Btw does it throw a code 33 when reved around 1/4 throttle ?

 

nope, on previous tests as well the SES light never turns on when the MAF is plugged in, despite the engine struggling, with the MAF unplugged i get codes though