1999 Toyota Tacoma SR5 with 320,000 miles

I have a 1999 Tacoma 3.4 V6 , I have cleaned the throttle body , changed the throttle position sensor and the idle air control valve and it still has a hesitation between the gas pedal on and off , staying at a constant speed it surges on and off..As long as the gas pedal is on or off it's fine , any advice please ??

 

Is your Check engine light on??

Have you pulled the codes??

No codes When was your fuel filter last replaced ??

 

Cleaned your MAF? Checked intake tube for a leak?

 

Clean MAF, replace fuel filter, replace spark plugs

 

Thank you guys for responding as I am new here and of course a little frustrated at this point..The check engine light is on but no code showing on the code reader..The last code was the throttle position sensor , which I have replaced as well as the idle air valve as well.. thanks I have changed the fuel injectors within the last 4 months , no problem after that..It just started this recently..Have cleaned the MAF , new plugs & factory wires , fuel filter , no vacuum leaks & it runs smoothly and great on the road , just a high idle and the dead spot is the best I can describe between the gas pedal on and off , like on a flat road keeping constant pedal and it like surges off and on , give it more gas and smooths out , let off the gas and it's smooth , just in between.. I have read that the throttle body could be worn out ?? 320,000 plus miles .. I can see light around the butterfly flap and some scoring around the inside of the throttle body where the flap edges stop when closed..Thank you again for your assistance and advice ..

 

Throttle body... maybe. I'd say a sensor, you've already done the cheap stuff. Going to go out on a limb and say maybe O2 sensors. I know you don't have a code but it's possible. Something is telling the engine to do something odd.

 

Thank you JJA04TACO .. I feel like it must be some mechanical issue since it's not throwing a code but the chk engine light is on & I clear it & it instantly comes right back on.. I did change both 02 sensors this past summer & of course I realize that is no guarantee 1 hasn't gone bad again..The truck does have over 320,000 miles now & it is running great other than the issue I have described here , it is one of the reasons I joined the Tacoma forum here as I know there plenty of Tacoma experts here & of course some guys like myself who know just enough to get myself in trouble..lol..One question about the throttle body butterfly flap..When it is closed is it supposed to be completely closed off as far as no bit of light can be seen around it & the inside should be completely smooth with no gap at all around the inside at all ?? Because I can see a definite gap around the butterfly as I can see a definite gap & plenty of light around it as well.. I think I read here that it should be completely sealed around this when it is closed.. I just don't want to buy & replace any more parts that are not the actual problem , because I am bad to start replacing things & when I get to the actual real issue I have ran out of money..lol..Thank you & thank you all for taking the time to read & help me out with this as I am at my wit's end on this one..

 

Mine is an 04' So it's different. But my understanding is that there is always a path for a little "idle air" to get by. Some have pin holes in the butterfly valve, some have little bypass ports or just stay cracked slightly. Could be yours is slightly undersized. Logic tells me that there is little actual wear and tear on the butterfly itself. There may be some ports, vacuum or "air bypass" for idle air to come in somewhere that could be clogged. I'm not too sure but I'd inspect it off the truck in case. Should be 4 bolts and a throttle cable and maybe a sensor or two.

EDIT: But if she runs and drives fine with a little hesitation especially on the road at speed, I still lean heavily on a sensor. That throttle body will be open at speed.

EDIT EDIT: If you have a CEL and there is no code you could have a pending code. Usually caused by something slowly going tits up, but not in the threshold for an actual code. That would be a sensor.

But usually an idle issue is an air/fuel issue. Either a mechanical issue like a fuel filter or an electrical/ecu ie a sensor. If you are sure the path for fuel is free and clear from tank to engine and it's getting there (like no burnt out fuel pump) I'd go electrical or sensor. An injector would likely be a constant issue, but could still be acting up. You can test O2 sensors (I forget exactly how) with a multimeter. If your really unsure have Toyota plug it into a diagnostic machine and get the data from the ECU. It's about a hundred bucks but could keep you from chasing your tail.

 

Just a suggestion . IAC valve gummed up. Idle air control.

 

Dear Johnny,

You certainly have done your homework with trying to get your 1999 Tacoma's 3.4 to start behaving itself again. From what you have said, you completely cleaned the throttle body on your engine as well as the idle air control valve. The important thing to remember about the throttle body is that it is a mechanical stationary part that does not wear. The linkages that control the butterfly valve and other linkages are the parts that wear. Now, if you are seeing some light by pass through the closed flap on your butterfly flap, I doubt that is causing the hesitation you are referring to in your post.

I think what you need to do is what Jim (JJ04Taco) has told you to do, and get the problem completely diagnosed before you keep throwing anymore money at the problem with the dealer that has the computer to get to the diagnosis.

Good Luck,
Paul

 

I had a 95 3.4 with 535,00 kilometers on it and after I cleaned the throttlebody I was having similar issues. Everytime I got on or off the gas it would hesitate really bad and also almost like buck slightly. It would also idle really high when sitting. Like 17-2000 rpms. It turned out that the gunk that I cleaned out of the throttle body was actually sealing up the worn out butterfly valve. The valve is brass I believe so it’s softer then the throttle body housing and does wear out after time. I researched and researched and tried all kinds of stuff, MAF, intake tubes, vacuum leaks, sensors... nothing changed it. I found a old thread on a website where a guy was having the same problem and he actually shimmed the bolt that the butterfly valve pivots on with a washer. I did the same on mine and it fixed the problem. You have to play with the thickness of the washer so you can get it just right. The butterfly valves gets off center in the housing over time and won’t close down correctly any more. I’ll see if I can find the link. Was a basically free job, just had to get a bunch of different thickness washers and try them out.

 

I was going through a similar situation where I was having hesitation, bucking and the petal had lag points with no CEL on my 00 3.4L. I cleaned the MAF (was a new cheap-o),new O2, TBS and TB, changed the fuel filter and air filter. Took a few months to get the light to come on and read a code (so I did have a code where you don’t) but eventually I bought an OEM (denso) MAF and the truck runs like new. Amazon prime exclusive had it at under 50 bucks and you cannot beat that.
Best of luck!
Jake

 

Does the problem get worse in warmer weather? I am guessing it is cold wherever you are right now.

 

I have the same issue. I have tried everything, EVERYTHING short of buying an entirely new throttle body to fix it. Mine is undriveable when the outside temp is higher than 80 F. No codes, no CEL. I had a Toyota mechanic look at it, and he won't bite on repairing it because even he doesn't know.

Edit: I can't even cast a vote above because I am so baffled.

 

Just to throw another possible wrench in the pile...I had a '99 3.4 doing the same thing, was hesitating and bucking at lower RPMs. Was throwing a code as if it was MAF or O2 so I did all of the above, replaced the O2 sensors and nothing seemed to work. Took awhile to figure out but after much angst and advice I ended up cutting the cat converter out and replacing it. Seemed there was just enough resistance in there to cause it to back up at lower RPMs. Ran like new afterwards, and was only $160 fix from the local muffler shop. Good luck.

 

When you first start your truck it should idle a little bit higher then settle. What does your truck idle at after a few minutes of running?

 

Try pushing in and out on the butterfly valve and see if it changes the idle

 

Was it random or all the time? I was good for months and then all of a sudden it did it again yesterday?... about an hour after I posted above haha go figure. Also a few hours after getting a car wash

 

My truck is a 2004 so it is a little different on the throttle body but here’s what happened with mine. I was doing some tlc on engine so I figured I would clean out throttle body and spray it offwith carb cleaner. Took it apart and when I put it back together the truck was idling higher than before. I figured I could just drive it around the block and it would be good. It ran rough and kept cutting out almost felt like it was backfiring, ran like crap. Got back home and took it all apart again put it back together then it idled low truck had hard time staying on. It had check engine light Idle air control fault so I ordered new valve. When it came in It was the wrong one so I looked at everything i took apart and noticed the IAC valve had yellow line where it should be lined up to. I started the truck loosened up IAC valve and moved it. Right away i noticed the rpms changed. There is not much adjustment but just tightening up the bolts would move it and make a huge difference. Long story short adjusted with truck on where it idled around 750 rpms and truck runs fine now. I’ve put about 3,000 miles with no problems.