I will start off with the basics. I have a 94 S10 Blazer with the 4.3l CPI vortec. Issues started a few months back with reduced power and hesitation. I have replaced everything fuel related including pump, filter, injectors, and return lines. It started to get worse and climbing hills was a challange so I had suspected the cat was plugged up. When inspecting the exhaust I found that the manifolds had cracks in them, and long story short, the whole exhaust was replaced from new manifolds all the way back and a new 02 sensor. Engine wise I recently just did the cap & rotor, plugs, pulg wires as well as coolant temp sensor and knock sensor. After getting this stuff done I could not get the truck to start and stay running. I had suspected the IAC valve as I had taken it out to clean. I found that the valve would spin freely and didn't seem to move right so I ordered a new AC Delco one. When I put the new valve on the truck started up and idled fine around 1000rpm. Once I put the truck in gear it would bog down and surge back up to keep itself going. I went for a short drive and all of the other symptoms had seemed to disapear but when I would pull to a stop it would want to die off. After this I could not get the truck to idle again. Suspecting the TPS sensor, i replaced this as well since the truck would run without it connected. Once the new sensor was in the same symptoms of no idle. I can take the IAC valve out and push the pintle back to its original location and the truck will idle for a mintue or so before it cuts off. I can not find any vacuum leaks but it seems like the truck is not getting the air it needs to idle. I can baby the pedal and it will run fine all day. Is there some adjustment with the IAC valve or TPS that I am missing as they seem to just be take off and put back on parts. Its almost like the computer is sending the wrong information and killing off all the air to the engine. I am not getting any engine codes and I was thinking to check the timing but I can't do that if I can't get it running to operating temp.

Any ideas? Crank sensor possibly?

 

Even tho you have changed out the fuel pump you have thrown parts at it and never did the most important step. Just because parts are new does not mean they are up to par.

Check the fuel pressers per sticky - don't skip any steps or do as most people do put the gauge on and start the engine.
This really don't tell you squat as there isn't really a standard pressure for running - too many variables.

If you have the scanner with the option do fuel trims .....

 

I have checked the fuel pressure multiple times. Key on I'm sitting at 60psi. If I start the truck and keep the pedal down a bit to keep it running it will sit around 55psi. After shutting the key off I will hold pressure at same level as well.

 

5 cents worth...

...check timing
...check ignition module and coil.

go back to the IAC. The pintle is hard to push in but should not have spots which are harder. Similar to compressing a shock.
Could be a sticky IAC.

The 94's unfortunately don't give up much information in form of error codes as they are pre OBDII vehicles.

Two times in 25 years my 94 (but with TBI) acted in a similar way. Both times were ignition related. Once out of timing, once the ignition module.
Would start, run until warm and not restart until cold. Similar symptoms have been observed on these modules. Running fine when cold and die when warm.

 

I have't had to much more time to look at truck but timing and the module were certainly on my list. The coil is new but nothing saying I couldn't have got a bad one, I may put my MSD coil back on and see. The new IAC is definetly working as it should as my old one would actually come apart when I just had it out and turned the key on to check operation. If i suspect the module I may just put in a new distributor as this truck really never had anything replaced as it was well kept up before I bought it.

Thanks for the reply.