HELP! I give up.

Small update: I have a new torque wrench and new intake gaskets. I played around a little last night but didn't take the intake off to replace the gaskets (didn't have that much time) but I did remove the upper intake so I could check the torques. I put the wrench on the front bolt and it turned about a half rotation before it clicked at 19 ft. lbs. That was enlightening to know that maybe my intake was under torqued and I might not have had the gasket evenly compressed all the way around because I didn't have a torque wrench before. So, I loosened all the bolts and went through the sequence and slowly tightened all 10 bolts until I achieved torque on all of them. It didn't cure the problem, but I think there was some improvement!!! This weekend I will remove the intake completely, clean all the RTV off and install the new gaskets. Hopefully this will resolve the issue totally.

NOTE: I did notice some oil in the front right intake. Is this due to bad air mixture? This is also the area where I noticed the undertorqued bolts.

 

Update, I'm at my wits end. I have done everything I know to do. I consider myself pretty handy at most things but this one has me stumped. Recap: I have changed the following with OEM parts: Injectors, spark plugs, coils, intake manifold gaskets and fuel pressure regulator o-ring. I still get lugging and mis-fires on the interstate at about 65 to 75 mph. It just seems like a fuel delivery issue. It runs perfect in town and anything below 60 mph. Once I go above that it misses and runs like shit. I have removed vacuum lines and checked them for leaks, scuffs, holes and rubs, nothing. I even loosened my gas cap to see if I had some issue with the cap, nothing. If any of you guys have any inkling of what this might be, please post. Note: I have absolutely zero codes.I guess I will have to resort to going to a dealer and letting them chase this goose.

 

Wild guess: clogged catalytic converter(s), or low fuel pressure at sustained high demand.

 

@Bebop any suggestions

 

Thanks, but the truck only has 60K miles on it. I would think that a clogged converter would be at higher mileage. I had a ranger one time that had a completely clogged converter and it totally shut down. My Tacoma runs great in town and even at accelerating but cruising at interstate speeds is where I see the issues. I appreciate the response and believe you me, If and when I find out what is causing this I will happily post the results. Everyone has been so willing to help. I love America!

 

Are you scanning only stored error codes, or transient/temporary error codes? The ECM processes three types of error codes: confirmed, pending, and permanent. It's possible for the PCM to report a pending error code (no check engine light), which then self-corrects. See if your scan tool can access all 3 error code types.

 

Jackpot!

 

I think you are referring to "Ghost codes". I have had the truck scanned for any codes and it is clean of any codes. Pending, or ghost. I really wish it would throw a code so I could stop throwing parts at it. LOL!

 

You'd need to scan for errors with a tool capable of reading and reporting Pending error codes while the problem was actively occurring.

 

I know there's no check valve on the 2nd Gens for fuel pressure. So I wonder if it's lugging or misfiring because you're putting a load on the engine or does it just do it because of higher speed (above 60mph)? If it's the knock sensor it will throw a code. I've dealt with knock sensor issues before. If it's putting a load on the engine regardless of speed, could be that the fuel pump can be clogged or going out so it's choking out.

 

I have always used brake clean or carb cleaner sprayed near potential leak sites when looking for intake leaks and listen for RPM changes. I had never heard of using an unlit torch and suspect that the air currents in the engine bay would render the torch method less effective than with the volatile liquid aerosols. I am on this this thread out of mere curiosity now. Anxious for you to get this fixed without further expenses and to hear what it took to cure the problem.
I admire your tenacity; I would have already threw my hands in the air and taken it to my garage buddy in complete and utter disgust.
If it is not a knock sensor, fuel delivery, or air/fuel mix (intake or vacuum leak) issue, I will be shocked.

 

Sounds like my old celica that had a clogged cat. Would only run up to 60mph and about 3k rpm before it fell on its face. Replaced the cat with a straight pipe and all was well. Also this is a common issue on the newer mustangs with low mileage. Shit happens.

 

What's it do when you hold the brake and smoke the tire (tires) and the rpms climb up there?

 

I appreciate your guys attention to this issue. In addition to propane, I also used carb cleaner at low idle and high idle to no avail. I've pretty much ruled out intake manifold leak. I'll be honest with ya'll. If this is something simple, I'll be very embarrassed and feel like a dumbass, but I assure you, I'll own up to it. I won't leave you hanging.

Christian06: I haven't performed a powerbrake on it because 1: I have bridgestone K02's on it at $250 a tire 2: I'm not so sure that it would do it. and 3: How would I diagnose it during such a manly move?

I think my next course of action will be to take it to the dealership and spend the $$ on a diagnosis. I can probably fix whatever the issue is a lot cheaper than they will quote me I'm sure.

 

There is a difference between loaded and unloaded resistance was thinking torque converter maybe

 

Dirty/faulty MAF? Those little wires can be super sensitive. I had a similar “high speed hesitation” on a VW GLI that was fixed by throwing the MAF element in ziplock w/alcohol to clean it up.

I also like the clogged cat theory.

 

I am a believer in the cat as well. I was think earlier today, that driving it around in limp mode couldnt have been very good for it.

 

Easier than checking for a pressure drop acrossed a cat, sometimes a good indicator of a plugged cat is to stand at the tailpipe with your hand a few inches away and have somebody rev the engine. Typically a plugged cat will throw out tiny sandlike particles that you will feel hit the back of your hand. Not a quantitative test, but a great indicator.

 

Thanks guys. I will check that out. Looks like they're two cats on these things. A front right and a front left. Also, not to question anyone's intelligence, but wouldn't I see an issue with acceleration in neutral if a cat was clogged? It accelerates perfectly fine in neutral. I do agree with some of the symptoms pointing to a clogged cat though. Haven't considered that at all since the truck only has 60K miles on it. I didn't do a great deal of interstate driving while in limp mode, just 45 to 50 mph in town.

On another note: Can anyone tell me what this part is? I knocked the little drum shaped piece off while working on it but slid it back on. It looks like a little vent. I didn't know if it had some sealing properties to it or not.