2000 Tacoma 2.4L. 150,000 miles. Excellently maintained, plugs, filters, etc. Running great one day then next day went to start and runs rough and won’t idle cold or when warmed up.
My scan tool shows no codes but adding way to much fuel (19%) even when warmed up.
where should i look first? Thank you
It’s very likely a dirty IAC (Idle Air Control) valve. The symptoms you describe do align with a dirty IAC.
I’ve had luck cleaning them, though replacing may be easier.
You can get a new one at: https://www.rockauto.com/info/724/215-2097_1.jpg
Thank you Joe. That does make sense. I’m going to order one. It might take me awhile but I’ll get back to you. If you’re like me you’ll probably like finding out if your educated guess was correct. Jim
Start the engine and slightly step on the gas pedal. Doing this takes the IAC valve out of the equation.
If the engine still runs rough it’s not the IAC valve.
Locate the fuel pressure regulator.
Remove the vacuum hose from the regulator, and if gas leaks out at this connection the diaphragm in the regulator has ruptured and allowing excess fuel into the engine.
Tester
This would fit with a bad regulator. Not enough fuel pressure, not enough fuel into the engine so the computer holds the fuel injector open longer.
If the above check out, what is the ECT showing when the engine is still cold, before starting does it match the ambient temp outside??
Definitely follow Tester’s triage steps for the regulator before considering the IAC.
Thanks Tester.
I just got back in from removing the idle control valve. I went back out and pulled the vacuum hose, no gas , dry.
When bringing it into garage it really didn’t run right even while giving it gas. I was going to try and remove the plastic electronic part off the valve and shoot it full of DeoxiT D5 but the 5 point fasteners seem to be an odd variety that I don’t have.
Usually I try to fix or rebuild first, been that way since working in the local gas station / garage back in the late 1960’s.
Thanks for all the help.
It’s apart now but if understand right. The coolant temperature when first started was outside temp and I watched it heat up to operating temp.
P.S. I belong to a few car sites and this website is the most difficult to respond to on my IPad. It jumps around all over the place. If I don’t respond properly please forgive me.
All vacuum hoses and lines connected and in good shape?
A couple more things. You could have a leaking intake manifold gasket or a crack in the intake manifold if it is plastic. A quick check of this is to spray all around the gasket with wd-40 or similar. If the idle changes at all, good or bad, it means there is a vacuum leak.
Another thing to do is get some MAF cleaner and pull the MAF and clean it. It’s worth doing even if it doesn’t fix the problem.
Edit: if your idle is higher than normal, say 950 instead of 750, that also indicates a vacuum leak at one end of the intake manifold, whether a gasket, crack or bad vacuum hose.
It’s not your iPad, it’s this website’s ads. My solution was to download DuckDuckGo and use it for all my browsing. If you do that, the ad space will be blank and the screen won’t flit around. Others say that an ad blocker eliminates the screen jumps too.
Follow up. First thank you to all. I cleaned carbon off the IAC valve shaft. Cleaned Throttle Body while in there. Started up. No change.
Then I remembered something I read long ago. Disconnect the MAS and see what happens. Immediately it ran great but at high idle. Cleaned MAS and now running perfect. Fuel trims perfect.
As stated before the truck ran perfectly, no codes, parked one day and went to start next day and immediately ran like ■■■■. Instant MAS failure.
( didn’t see Keith’s MAS cleaning suggestion until just now)
