My 89 toyota pickup has a loping idle after it warms up. i have no check engine lights on and when i step on the brakes it slows the pace of the loping idle. Vaccumm line from the brake booster was my first guess i check it out but it seems fine. any one got a clue? and i bought a new tps sensor but i dont want to put it on if i don't have to.
I had the same problem and found the idle screw was hitting a small shock absorber that had worn out and wasn't allowing the rocker arm to release all the way. Now i just need to find a replacement part for this 20 yr old truck, right.
Its a vacumm guys check all your hoses with a carb cleaner while engine on be carefull not to let it catch on fire with the spray ok give it a slight of puff of it with the spray ok!! remember truck hoses are old and cracking ..
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The Idle Air Control Valve (IACV) may need cleaning or replacement.
This valve lets air bypass the throttle plate so that the engine can idle. The more air, the faster the idle. If this valve is sticky, the computer may have a hard time regulating the idle properly and may surge.
Could be a throttle position sensor going bad or a loose or leaking vacumm line or loose or worn wiring harness. You had mentioned the engine starts heating up. Do you mean overheating or operating above normal temperature? Sounds like a vacumm issue with the fluctuating idle. Check for worn vacumm lines and check to see if the vacumm is functioning. Sometimes a simple vacumm line with a loose connection or a small hole in it can affect your idle. Old lines are easily replaceable and an inexpensive place to start, then try your egr valve, pcv valve, brake booster vacumm line, oxygen sensor could be worn and affecting the mapping of fuel and air on the computer. Usually the check engine light will come on in this case.
possible egr valve problem,you can start with disconnecting the vacuun source to it and see if it rubs better but if its stuck open you may not notice any change,you can look underneath the valve with a light and mirror and apply vacuum to the valve and watch for the diaphram to move up and down,have you checked tec ecu for codes? if you need more info let me know have a good day DB
1990 22re same problem surge when pedal was depressed thought it was booster or check valve still didnt fix it i even put a brand new booster on it just to make sure still no fix it finnally went away on its own for about a month now it does it just sitting at an idle with out the brake pedal depressed traced all vaccum lines no problem there and still have no clue