Cranks But No Start & Idel Speed Varies

[DixieWASP]

Yesterday my truck would crank normally but not start. Everything was fine until I tried to start the truck after sitting for about 20 min. On the third or fourth attempt to start the engine, I depress the accelerator pedal about 75% and the truck started but immediately died when I put the truck into reverse. This happened three times. I finally got the truck to rev in park at about 2500 RPMs for a good 30-45 seconds before I attempted to put the truck in reverse. This time the engine did not die when I put the truck in reverse to pull out of the parking space. The drive home was normal.

For the last few weeks, the truck's idle has been high and then on other days the idle is normal.

My truck is a stock 1989 Silverado with the 350 V8 and TBI. I replaced the distributor, cap, and rotor along with a new EGR valve two months ago. About six weeks ago I replaced the fuel pump and fuel filter.

No check engine light and the idle is very smooth.

Any thoughts on what to check? I need a reliable truck that I can trust.

 

[Dariusz Salomon]

Could be a throttle position sensor failing. I had a similar issues in jeep-but then it would not shift through all gears and fuel consumption was crazy. Idk how does it works in those older trucks tho-mine is 99. Just a thought.

 

[Schurkey]

Connect a scan tool, find out what the computer wants you to know.

I'd be looking at TPS, IAC, coolant temp sensor to start with, but verify EVERY sensor and computer output.

How old are the spark plugs, plug wires, air and fuel filters? Will the ignition coil fire a spark-tester calibrated for HEI ignitions when the coil is hot and the top is sprayed with a windex-style misting squirt bottle?

 

[DixieWASP]

Connect a scan tool, find out what the computer wants you to know.

I'd be looking at TPS, IAC, coolant temp sensor to start with, but verify EVERY sensor and computer output.

How old are the spark plugs, plug wires, air and fuel filters? Will the ignition coil fire a spark-tester calibrated for HEI ignitions when the coil is hot and the top is sprayed with a windex-style misting squirt bottle?

I removed one spark plug and it was in good condition. It showed little wear and the color was tan. The fuel filter is almost new. Not one full tank of gasoline has been run through the new Wix fuel filter. The air filter is clean and in good condition. I have no idea about the age of the plug wires but I would feel better replacing them so I know that is not a problem. I will check the ignition coil.

Thanks for the suggestions. My shop teacher has an OBD I scan tool that I can connect to my truck when classes resume on May 25.

 

[Immisterfixit]

I removed one spark plug and it was in good condition. It showed little wear and the color was tan. The fuel filter is almost new. Not one full tank of gasoline has been run through the new Wix fuel filter. The air filter is clean and in good condition. I have no idea about the age of the plug wires but I would feel better replacing them so I know that is not a problem. I will check the ignition coil.

Thanks for the suggestions. My shop teacher has an OBD I scan tool that I can connect to my truck when classes resume on May 25.

Did you find and fix the issue?

 

[DixieWASP]

Did you find and fix the issue?

No, did not because luckily the truck has had no more issues. I did connect a Snap On OBD 1 scanner and everything was normal.