'93 Sierra No Start Problems

CGiff9 · August 8, 2011

First post!

So about three months ago, my '93 GMC Sierra was getting gradually harder to maintain after starting. Eventually, the truck wouldn't even stay running on it's own unless the gas pedal was depressed, and even THEN it was erratic, and the pedal would have to be pumped to keep the engine running. It was in an un-drivable condition.

After dad and I threw a fuel filter, an IAC valve, and a new fuel pressure regulator at it, we finally decided to rent a fuel gauge. We would have bought one, but this TBI system has no schrader valve to attach a tester to. We tested the fuel pressure, and we got nothing. We went to NAPA and bought an aftermarket "Carter" fuel pump, installed it, and voila. Truck ran just fine for three months.

Now it won't start, and appears to be exhibiting the exact same problem. The starter turns fine, but the car just doesn't stay running. I did notice that before the truck reached totally no-start condition, it would idle extremely low, as in the tachometer would be at practically zero. My first though was "Oh no, it's the crappy aftermarket fuel pump dying on us." We snapped on the fuel gauge and when we turned the key to accessory, we're getting a good 14 PSI. We are also getting 14 when the truck is running (again, by pumping the gas pedal erratically to keep it alive).

We ARE getting an error code. OBD1 error code 35, faulty IAC system. How on Earth, when the IAC valve is a mere 3 months old? What's the problem here?

Dad needs the truck soon, and we'd love to be able to park cars in the garage, which seems to be an impossibility... Thanks everyone!

[email protected] · August 8, 2011

Sounds like a vacuum leak too big for the iac valve to control to me, look around the TB and whatnot or spray some water or ether and see if the idle(running condition as a whole) fluctuates.

CGiff9 · August 8, 2011

Sounds like a vacuum leak too big for the iac valve to control to me, look around the TB and whatnot or spray some water or ether and see if the idle(running condition as a whole) fluctuates.

Actually, I think that the opposite of a vacuum leak is the problem. I disconnected the tube that leads from the PCV valve to the front of the throttle body, and the truck started by itself and stayed running. Does this mean there is some kind of obstruction in the TB, or perhaps some other valve/component is stuck shut?

I also replaced the IAC valve because I took it out to spray it with some carb cleaner, and when I put it back on, I tightened it way too much and the thread part just snapped off the valve. Luckily my dumb arse didn't strip the threads to the throttle body. $40 mistake right here! But now, after a quick battery reconnect, no more Error Code 35 (although we may not be running the truck long enough to generate one).

So, is this really a vacuum obstruction?