87 Idle/Offline probs

[k20]

When I start my truck (cold) it runs fine. Once it heats up it starts going low and high idle, almost like its got a huge cam in it. You can visually see the accesories slowing and speeding up. Also at a stop sign when i get back on the gas it will bog down and have no power until you hit 10ish, then it will take off. However, it doesnt do this constantly. Checked all the wires they are fine, check plugs, theyre fine, the rest of the ignition system was changed in late jan or early feb. I sprayed some carb cleaner around the base of the TBI when it started doing this today and one side of it kinda steamed off. Does carb cleaner usually steam? Other side (in the sun) i didnt notice it steaming off, just evaporating... Could this be a bad gasket causing a vacuum leak, and therefore this prob. Also the off the line deal doesnt happen everytime, just most of the time. However the part of it idling bad happens evertime once it heats up. Thanks for any ideas on what may be wrong, just need a patch for a few weeks or a month, and by then maybe my new engine will be ready...

 

[blasterD]

Did you check for any trouble codes?

 

[k20]

yeh it has no codes.

 

[bassmannh]

It is very common for the tbi gasket to be bad,very easy to change. but is also just as common for the IAC, idle air control solenoid to be carboned up,it is in the left rear of your tbi when viewing it from the front, get a step and look down inside the left rear and watch for the plunger to move when you move the throttle,( be very careful to have good footing so you dont slip and get the air cleaner stud in the EYE)it should be nice and clean (no Carbon build up)you can spray it with throttle plate cleaner or carb cleaner while reving up the engine so it wont stall, the other thing you might want to check is the egr valve opening to soon,causing a tip in stumble or hesitation,rough idle or all of the above.Try disconnecting the vacuum tube from the egr and plugging it and see if this doesnt change the way your engine runs, Good Luck /forums/images/graemlins/thinking.gif

 

[k20]

I changed the IAC at the the end of jan as well forgot to mention that one. Also does carb cleaner steam when it evaps? (usually use brake cleaner for stuff but figured it would evap too quick) Or could that steaming be vacuum leak? Ill try the egr tomorow, when you say see if it changes it, should it make it better or worse lol? Still learning this computer controlled crap...why didnt i just get an 86......

 

[Grim-Reaper]

Unplug the EGR when it's still cold. It should throw a code after about a mile of driving above 1500 RPM. Ignore the code and see if the problem still there. If the EGR has a control solonoid like my 454 my bet is it's that control solonoid.

 

[bassmannh]

If the egr is opening to soon it will lean out the engine and make it stumble, it should run BETTER if this is the case. You might set a code 32 after driving at 55+ steady throttle and the computer looks at set perameters in the block learn of the integrator,also you might get some slight knock sensor activity, but nothing to worry about if your knock sensor tells the computer it senses knock, the computer backs off the timing in the electronic spark controll a couple of degrees at a time until the knock goes away. Also there might be an updated prom for your computer involving egr problems,hesitation and early tcc engagement. My 1987 K5Blazer 350TBI,700r4 truck has the 9931 prom ID# in the snap on scan tool, and the GM prom cross reference book from snap-on shows an updated prom that is supposed to cure all of these problem, plus cure extended crank times at start up under all conditions. Hope I didnt give you too much to think about.