99_Runner

Did some searching this morning and didn't find anything exactly like mine, or even similar.

I'm having a "miss" or hessitation under 1/4 or less throttle. If i get past that to 1/2 throttle then everything runs fine. If I floor it then it runs fine, even from a stop light. Here's what I've done:

Replaced all injectors
Replaced all spark plugs, old ones had less than 30k on them though
Replaced 1 coil as I confirmed 1 was bad by moving it around and the misfire code followed it

Fuel filter was replace less than 30k ago as well.

If I never use partial throttle then everything runs fine. This is hard to do in traffic and while trying to maintain speed on the highway.

Any ideas?

cpizzle42

Any engine codes? I assume you atleast had a misfire code? Is that code cleared?

How is idle speed? Is it high? If it is too high due to a vacuum leak, it may be causing your fuel pressure regulator to be giving your rail to much fuel, causing the hicup.

rworegon

Dirty MAF, TPS issue, vacuum leak....

Ground wires all tight?

J2F42C

+1 with rworegon on checking the TPS. If you know someone with a Scangauge, it can be done.

How about the 02 sensor(s)?

Are you filling up at the same gas station?

awdjunkies

Perfect way to find your culprit, Process of elimination. Also, OP thanks for giving out as much info as possible in order for others to help find a cure.

99_Runner

I was getting P0301-5 at any given time. Those codes are cleared. Kept coming back with P0171, so I cleaned the MAF last night. Idle seems good, about 700 in gear.

I did find one ground wire that I forgot to hook back up after doing the injectors. I reconnected it last night, along with cleaning the MAF. The TPS was the first thing I replaced, sorry for not including it in the original message.

I don't know anyone with a Scanguage, but I'm in the Denver area and would be willing to drive anywhere in town if somebody was willing to help me out. Not sure on the O2 sensors as it's never thrown a code for them. Different gas stations from all over town.

Thanks. It's been a while since I've been on here, but I know it's frustrating to give help when somebody comes on and says, "I'm having a problem, what do I do" but don't give any info.

Thanks for all your help guys. Even after cleaning the MAF last night, and leaving the battery disconnected for 10+ minutes to reset the ECU, it's still doing it this morning, though not as bad.

Any other thoughts?

rworegon

Have you cleaned the throttle body and IAC valve? Dirty air filter?

Lycanistic

Call it a stupid question, and forgive my ignorance on this one, but does the 3.4 run a fuel pressure regulator like our 3.0's? Could that be a cause of the hesitation? I modified mine to run full pressure at all times, loose a few mpg here an there, but love the gain in low end torque.

J2F42C

How about plug wires?

If your TB/IAC has never been cleaned, especially the former, I'd start there.

99_Runner

Plug wires were replaced when I first did plugs about 30k ago.

I cleaned the IACV and the throttle body this weekend. Now it's running worse and throws the P0120 IACV code all the time. Could I just need a new valve?

rworegon

P0120 is TPS, not IACV per FSM:
http://www.ncttora.com/fsm/1996/SIL/...fe/cip0120.pdf

99_Runner

Correct, my bad. I replaced the TPS first. Is it possible to get a faulty one?

rworegon

It could be bad...go through the diagnostic on it. Could be a bad wire too. There are several P0120 threads 'round here.

No problem on calling it a IACV error code.....just wanted to get it corrected before you possibly were headed down the wrong track.

99_Runner

Ok guys, really pulling hairs now. I went through the tracing of wires per the FSM. It shows that I should have 5 connectors plugged into the ECM. I only have 4. The middle one isn't there. Is this normal? I tested what I could and everything was within Toyota spec. Not sure what to do now.

99_Runner

Bump. Any ideas guys? Don't really want to take it to a mechanic and have them not be able to figure it out either.

I'm starting to lean towards the IACV as it will "miss" even when in park. It also does it bad when coming to a stop. The TPS checks out to Toyota specs, but not sure. I can get a new one, but once I put it on I can't return it. Don't really want to spend another $60 on something that may or not be needed.

One thought I had was to get a TB, including TPS and IACV from a junk yard. Swap the whole thing imams see what happens. Finding one is proving to be fairly hard though.

99_Runner

Ok, last shot before I either take it to a mechanic or just sell it broken. I love this vehicle but can't figure this out. Here's a breakdown of what's been changed:

1. TPS - from O'Reiley's
2. Injectors - brand new from Rock auto
3. Replaced 1 coil that was bad
4. Spark plugs - OEM from Toyota. These replaced the OEM ones that had less than 30k on them
5. Cleaned IACV - this seemed to help, but now the check engine light never goes off
6. Traced wiring per FSM. Everything seems to be in order, though see above post

A constant P0120 - TPS code is now being thrown. I clear it and it comes back on a few miles later. This would be ok if I had a test TPS to put on it and see if that fixed the issue. However, none of the auto parts stores will let me return the TPS once I've put it on the vehicle.

Anybody in the Denver area work on Toyota's and want to take a look? I went to one of those U Pull & Pay places to get a whole TB setup, but they didn't have any.

Throw some ideas out there guys. Really need to get this fixed as I can't really afford to buy a new vehicle right now.

Kiroshu

If you have proper voltage going to the TPS then more than likely to rid the check engine light is the TPS. I've seen alot of faulty TPS's off the shelf before. I had one customer come in a while back with a truck and they said they just put a tps on the truck but the truck would bearly run and would nearly cut off on acceleration.

Computer threw and code for the tps and when i took it off it literally fell apart in my hand. Showed the customer and they were suprised. Replaced it... never saw truck again...

Possible weak fuel pump? Check fuel pressure? You said it was throw the 171 lean code before? Thats a pretty good indicator of things.

Vacuum leak..
Timing belt off..
Low fuel pressure...
Improperly gapped spark plugs..
Dirty air filter...
Dirty or faulty mass air flow sensor...

99_Runner

Ok, I replied to some of your thoughts above. I'll see if I can get a TPS from somewhere else. Maybe Napa or Car Quest. Oem is a little too steep for me, though maybe Rock Auto has one that would work.

Kiroshu

Vacuum leaks unless heard or visibley noticeable are not sometimes easily detected. If a large leak is present then engine would idle high as the engine computer is trying to compensate for this unmetered air entering the engine.

Vacuum leaks can also be discovered using a smoke machine...

You can check engine vacuum with a vacuum gauge and see if the engine is "healthy" normal engine vacuum depending on the vehicle is between 18-22hg.

Believe the 3.4 has a closed fuel system... so tapping into the lines with the proper fuel pressure testing equpitment will be required...

Mass Air flow sensors are very delicate and sesative to debris touching the sensing part of it. Its normally unwise to ever clean the sensor cause it can damage it and cause faulty computer readings... they do however make the special cleaner for them. I would recommend cleaning it only as a last resort even with the cleaner. A dirty air filter element that is no longer functioning as a filter due to it being past its service life allowing debris into the sensor can damage it as well.

Kiroshu

Lots of variables... but you are on the right path...