Idle problem

[Brandon5474]

I have a 1994 K1500 5.7 TBI and I can't get it to idle correctly, after the truck warms up when you are sitting in park the rpms gauge will slowly drop and start bouncing a little bit and then rev back up for a couple seconds, you can hear the engine speed up as well as you can see the rpms go up and then it will go back down and it will keep doing it repeatedly. It is like the idle changes on it's own ,does it in drive too but it's not as noticeable. Only code I get is when I drive on the highway I get a code 44, any ideas?

 

[joep88cheyenne]

Try spraying wd40 around your vacuum lines to see if it runs up in idle, if so where the spray was last would indicate a leak, hose off or cracked hose.also around the base of the TBI spacer, and TBI base. Eliminate some simple issues

It could be inconsistent fuel flow, like filter or dirty spray heads.

 

[DerekTheGreat]

My truck did something similar to that. Only it would often idle correctly for a bit and then suddenly start acting up. When I hooked my scan tool to it (FapOff MT2500) I looked at the data for a good while and noticed that when it acted up, the TPS voltage was fluctuating erratically without me actually touching the accelerator. It's programmed into these things to adjust the idle up (At least with manual transmission trucks) when you step into the gas. Swapped out the TPS with a good one and it's been perfect ever since.

Now, seeing as you've got code 44 going on (O2, lean mixture detected) it's possible you've got a vacuum leak. Could also be a wiring/ground issue too. So you could look into those things first or acquire and hook a scanner up to it & see what's going.