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1994 K1500 Suburban with a TBI 350

I just bought this thing and it has a surging idle. The idle will vary several hundred RPM at a frequency of a couple seconds between surges. It sounds like the engine almost dies then springs back to life. The vehicle ran fine then this problem just started.

The check engine light is off.


If I unplug something, like the wiring connector for the MAP sensor, the engine will idle fine. Would this tell me that the spark and fuel pressure are good?

The previous owner replaced several parts instead of testing them, then brought it to a GM dealer who couldn't fix it either.

Parts he replaced, none of them changed anything:

IAC
TPS
02 sensor
EGR (from a junkyard, so it may have ben trash too?)
EGR solenoid
Cap, rotor, plugs
MAP sensor
Temp sensor
PCM
Spark module? (he said it's inside the distributor)
Checked extensively for vacuum leaks

I haven't checked for vacuum leaks, but plan to soon.


From searching the forums, I checked the alternator voltage and it was 14.3 volts. The truck has an MSD coil, but I don't know how to check for 13.8 volts on the red 10 gauge wire. And it runs fine with the map unplugged... so the coil may be good anyway.

Edit: I checked the timing also... it's right on 0*.


Where should I go from here?

 

Ok, I went through a tall can of starting fluid, spraying on all vacuum hoses, throttle body and gaskets, and intake gaskets and found no leaks.

The engine has rapid fire plugs and an MSD coil... I'm going to check them when I get some time. The engine seems to have a miss when revved up too.

It smells like it's running rich out the exhaust.



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