Tbi 350 Idle And Miss Woes

awalkertx · December 7, 2007

Hi all,

I've had this truck for 10 years now, and over the past 6 months it's developed two problems that i'm not convinced are related. It has the L05 TBI 350 and MG5 manual transmission. ~200k miles. I love this truck, and if the engine didn't have good compression, i'd have already transplanted an L31 into it.

MISS PROBLEM(started a month ago): Engine will miss under a load above 2000 RPM. It is clearly be seen on the tachometer... the RPM will jump up 500 to 1000 more and then drop to zero. I replaced the plugs, wires, cap/rotor, coil, pickup coil and ignition control module... engine timed to 0 degrees TDC per the sticker on the fan shroud. The truck acceleration is considerably better (and my AM stations work without a ton of RPM-dependent interferance); HOWEVER, the problem still remains. The miss is less pronounced but still there... more like it will jump +/- 500 RPM when the truck goes over about 2200 RPM.

IDLE PROBLEM (began in the spring): The truck when cold will start up fine and high idle (~1100 RPM on the tach), then warm up to a normal idle (~700 on the tach). If driven a while and then turned off, then restarted shortly thereafter, the engine will die unless I keep some right pedal in... It's like it doesn't even want to try to idle. I can drive it around at this point, but more often than not need to keep a little gas pedal in when I come to a stop. I can partly alleviate the idle problem by inducing a vacuum leak (pulling the large vacuum tube off the font of the throttle body), which is no way fixing the problem. EGR valve is only a few years old, and acts fine when depressed and the truck is cold. I had a MAP HI code a few years back, but that's no longer being flagged.

any ideas? thanks for any insight!

Adam

PS, I don't want to add that it has an Edelbrock MPFI conversion on it, which has been fine since 2001 and uses all of the original sensors and throttle controls... looking for a more basic issue/fix before I swap the old stuff back on.