2001 tacoma 2.7 pre runner idle problem up and down

So I read all I could read on this problem that I have. We replaced the fuel pump because the truck wouldn’t start. After ruling out all fuses it ended up being the fuel pump. We did the spark plugs before the pump. Truck started right up. So it was the pump that gave out. On the first start we noticed it was at high rpms. We thought it needed to adjust itself after we sprayed it with starting spray. But after 2 days of use it’s still doing it. At idle it’s like 2000rpms. When you shift to drive they go up and down on their own. Got A CEL and a P0110. Which pointed at the MAF sensor. We replaced it and it’s still doing it. We did a smoke test and nothing. Anyone have any ideas? I tried to rule out everything I could by reading on here and nothing. Weird part is that it was running fine before the fuel pump gave out.

 

Maybe check your throttle position sensor.

 

Clean the tb and iac

 

https://www.youtube.com/watch?v=agIRNNA-6cs&t=2195s

 

Next step would be to scan it and watch the maf numbers...
engine temps .....ect sensor...

then throttle position sensor data.....


these engines are pretty simple......but they don't like non-oem engine sensors...

you know the ones they sell for 1/10 the price of the real ones.....

 

A scanner that reads live data....can take a lot of guess work out of it...

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Well we did all of the above. Throttle Body cleaned out and left super clean new gasket. Cleaned the IAC installed with a new rubber gasket. Checked all the vacuum lines, replaced a couple of worn out hoses. After we put everything back together I checked the screw that stops the cable to the accelator. So I adjusted it to see if I could lower the acceleration. While messing with it we noticed that now the rpm’s were fluctuating with each movement of the accelerator. We checked the pedal for any obstruction nothing. While tightening the nut to the screw mentioned above I pushed down on the accelerator and it dropped even more. That’s when we figured out it was that component in the picture. When pushed all the way closed rpms are at like 750 at normal sitting idle.

 

So it was a weak return spring as the cause?

 

Yes. Or at least that’s what was causing the high idle. I push it down with my hand and it drops to a comfy 750. I just don’t know if they sell that part by itself or it comes as a whole unit on the throttle body.

 

Try a little wd-40 spray on the spring, just to lube it.
Maybe that'll help smooth it out

 

I did hopefully that helps it. I’ll see in couple of days. The black plastic besides it, against the TB seems like it’s loose or possibly broken off it’s original position and maybe that’s getting in the way of it returning completely back to home position. I’ll give it a week to see how it does with the wd-40. What I did like is that I was able to lower the idling rpm’s by adjusting that hidden screw. Since we bought it for my son it has always had a hard shift when shifted into drive or reverse. Now it’s a smooth shift. hopefully I sniped the gremlin this time.

 

Its very unlikely but....

there was a thread where the TB butterfly wasnt closing all the way...

he determined that the vacuum dash pot was keeping it from closing all the way...


Here's a simular....but an electronic one instead of the older vacuum one...

worth investigating......

UPDATED: Part ID Question -- Dashpot | Tacoma World

 

I also just encountered idling issues on my truck, turned out to be a bad upstream O2 sensor (bank 1, sensor 1). I wound up replacing both upstream/downstream O2 sensors, cleaned the MAF, and she's purring now with now codes thrown, and no more idle issues.

I know you said you replaced the MAF, but you should try spraying it thoroughly with CRC Mass Air Flow Sensor Cleaner anyway. Just farting in the general direction of a 1st gen will adhere it, and all the gunk stuck in the air filter to the MAF causing dolphin RPM issues or plain engine non-starts.

 

I've also heard of the butterfly would slide forward and back in the TB causing hard to find fluctuations...

Thread on this about 6months ago.........but heard only of it once or twice over many years....very uncommon....


I understand.....these are just reaches.....but something to check..

 

We did all that. It seems to be the return spring on the accelerator cable component on the throttle body. If it’s idling high pushing it back down by hand it goes back to normal. I did spray some wd-40 on that spring area and someone also recommended that on here. For now it seems to be working and purring like a new tacoma‍. Son drove it back to college today and said it worked great mpgs are better he said. We lowered the idling rpms by adjusting the set screw and nut as it had a high idle ever since we bought it for him. It was used but in very good condition for only $950 and I say $950 because the man said just give me that so you can buy a good battery for it.‍Smh/lol.

 

Another long shot....is the throttle cable or cruise cable is binding or jacked...

 

I thought it was the cable at first but no. They both had slack while making its full return.

 

Funny thing is....I bought a backup salvage TB for my year......just because I was worried about that exact spring...
ultimately for those of us that will get buried in ours.....that spring will eventually fail...

maxbore can fix and install a new bigger butterfly...but that spring could be something they cant fix....

 

Right on. Good job!