RPMs 0 - 1200 - 3000 - 1200 (1 Viewer)

Truck = US Spec, 1997 Petrol FZJ80 with supercharger, beater edition in buggerville

RPMs are dancing back and forth rapidly when the truck is in D or N, P and everything else. Acts like I'm there just pumping on the gas pedal. Also does so, although not as bad when driving it.

Stopped by the dealer and he put a scanner on it for me indicating the TPS was staying on all the time. He walked the IAC through the various steps which should shut off the IAC but to no avail.

Here's the full history:

About 2 months ago, replaced the full exhaust from the manifold (had to drop a bolt in where one of the studs had to be torched out. Anyway, went with discount converter cats with associated tubing back to flowmaster 50 muffler and on out (no resonator). About 2 weeks after this, I formed an exhaust leak between the 2 cats (the gasket was destroyed). I then looked under there and saw one of the bolts holding the 2 cats together came out. In the mean time, since this happened while on family holiday trip, the truck started running like crap. At 2,200 RPM it was fine but at 2,300 RPM the truck would dump fuel and pump it up to 3,300 RPM quickly and bounce back and forth till I would drop it back to 2,200 RPM. Exhaust shop looked at it, to figure out why the gasket was fried up and they said it was running too hot (could be due to the dumping or it could have been before I don’t know, but the exhaust is purple ½ back through the muffler now). Anyway, they fixed the leak and sure enough my other fuel dumping issue went away. I presumed this somehow related to the exhaust missing the second O2 and hence thinking it was lean was dumping more fuel etc. {note all this could be unrelated to the below, but maybe not).

About 1 month ago I developed another leak. Now it’s where it bolts to the manifold. Also about 1 week ago it started messing with the 3rd and OD while driving on back roads. At times when it seemed like it should drop to OD it would stay in 3rd with higher RPMs than normal. Then about 5 days ago it got to the point where when the truck starts, it goes right to 1,200 from 0 then bounces to 3,000 RPM like I’m pumping the gas even though I’m not. It does this ‘pumping’ while the truck is in P, N or D although not as bad when in D. Much worse in D when at a stop light than when driving. While having this problem, I took it to the dealer who walked it through the above TPS/IAC steps. He thought maybe it was the IAC so I ordered one. In the mean time, I took the truck back to the exhaust shop. The gasket that goes on between the pipe and manifold had burned up all the paper and they told me the exhaust was way too hot. They said it was likely due to the idle issue. Checked out the IAC yesterday. In addition to the one I bought, I borrowed one from a working cruiser yesterday. I swapped in the non-new one last night, and no change. Still have the prob. Also found a vacuum leak, replaced the hose that goes from the T under the supercharger crossover pipe to the throttle body. Still no change.

So I’m now completely clueless (never had one anyway as most of you know), but any ideas on what this could be? Could this all be related?

I hate my truck and apparently it now hates me too.

Throttle Position Sensor Bad. That's My Vote. BTDT on my 4Runner, fixed the problem promptly. HTH.

Sounds like something with that TPS or the wiring to it.

Good-luck

I would tend to agree with turbo and tank check the TPS but as screwy as this problem sounds I would be curious as to what Robbie thinks especially with a supercharger on the rig as that probably complicated things.

reffug said:

I would tend to agree with turbo and tank check the TPS but as screwy as this problem sounds I would be curious as to what Robbie thinks especially with a supercharger on the rig as that probably complicated things.

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Good point, I would think the effect of the supercharger would be to peak the rpms somewhat higher than with the normally aspirated engine. On my 4Runner when this happened, I had the exact same symptoms and went through many of the exact same checks for vacuum leaks, exhaust leaks etc. The only difference was that my rpms peaked at about 2200 as opposed to the 3000 or so that Junk is getting. That could be the different engines of course, or it could be that as the TPS is changing the voltages so rapidly the supercharger is pumping up the rpms. Just guessing but I think its an educated guess. Another thing I learned was how precisely the TPS must be adjusted; its a PITA to hold the feeler qauges, the voltmeter, the TPS and the screwdriver just right. One trick to help the diagnosis is wait till when the oscillations start up ( mine were intermittent) and then lightly tap the TPS with the handle of a screwdriver or something. If this momentarily stops the oscillation, then you got the answer. HTH.

reffug said:

especially with a supercharger on the rig as that probably complicated things.

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Just what the guy wanted to hear

Junk,

The concensus seems to be that you should remove the SC and send it to Beowulf@PayPal.com

PM the tracking number when you get a chance.



-B-

I do recall him sayin something about being tired of it. Or was that someone else......

Beowulf said:

Junk,

The concensus seems to be that you should remove the SC and send it to Beowulf@PayPal.com

PM the tracking number when you get a chance.



-B-

Click to expand...

you can buy it at any time providing you provide stock replacement bits that I tossed away :whoops: during the last move. not much $ at all.

tried whacking on the tps and off onto it but neither seemed to do much. Running the IAC through the steps should make the TPS click off, but it's staying on full time apparently.

Still not sure which came first, exhaust issues or fuel, but it seems that one impacts the other.

Just had my throttle body cleaned out. Was idling rough and rpms were dancing similar to what you describe. Very smooth now.

Sounds like you have bigger issues - but then we all know that. hehehe

Hey Mike: First thing I would do is to fully check out the TPS against the FSM to see if it is fully in specs. With the throttle body gummed up it could cause the TPS to stick in the open position if the TPS was set on the senstive side. So check the TPS if it is bad, get a new one. Also if it is good, readjsut it. these are a printed circuit board style sensor, hard to screw it up. I would also check out the wire in the harness going by the EGR pipe. If there is any indication of heat or the harness lying on the pipe, pull this harness apart and check for melted wires. It maybe that you have melted some wires that are touching and could create more damage if left alone. The other place wiring harness can chafe is behind the glove box, just behind the computer as it makes a sharp turn.
I think you have a problem that is creating your fuel management problems laeding to screwing up and overheeating the exhaust system(too much fuel). If not taken care of the truck could go up in flames at the wrong time.
So check the TPS, throttle body, wiring harness in that order before ordering any parts. You have not washed your engine compartment latley or gotten it wet? If so you may have water in the connections of the TPS and The IAC, if water is in these connection, it can create similar problems. Later robbie

Was thinking about the SC install a bit, did your installer cut and splice all the connections or jsut a couple to lengthern the wires going to the TPS and IAC(these are moved in the install). I would also check any and all of these connecion for frayed area that allow contact between two wires, this has the potiential for makeing the computer fry, thus costing some good money to replace(do not ask how I know). later robbie

Mike,

I saved all my '97 OEM non-S/C parts when I did my install. If you really want to reverse it, let me know.

Robbie -- I lengthened and soldered all my connections. Should I be worried about this and redo them all? Or should I be okay?

soldering is ok in my book, the problem was that some of the spikes of the solder and or little sharp hairs of copper poke through the cheaper shrink wrap we use in the past. Since then we use milatary spec shrink wrap and double it. Better to be save than sorry or lose money. solder vs crimping has been discussed to death in the past with camps on both side. It really is what you perfer as long as you insulate well. later robbie

Thanks for the help everyone.

Scamper - will PM you about your original bits. Taking this thing off would be a nightmare I suppose.

Robbie - Have not been in any water or mud in loooooooooooooong time. I'm pretty sure all the wires were lengthened, but will find out after I pull apart the harness. Thanks for all the help as usual. Will take out the TPS, clean throttle body, check wires. Not sure where behind the glove box, you mean right before it goes through the firewall from enginebay to interior, or actually inside the dash?

THANKS

The computer is bolted in a different position in later years, lower then the old one. SO the wires make a shrp bend around some metal just after the computer behind the glove box. you will easily see it. lenghting all the wires sometimes will create problems if not done right. I only lengthed the power wires any more to lessen the chances of problem. The power wires for the IAC are spliced into the Wiring harness instead of a fresh run from the computer. Later robbie
In the 91-94 crusiers the computer were mounted higher above the glove box, where the 95-97 computers were mounted level with the glove box. In fording streams this could be the difference of getting across the river or not.

Junk, I've no experience with installing the SC but if you want some help get in touch with me. I'd imagine the biggest pain is the crank bolt and I have a tool for that now.

Hey Junk look over every thing first, look at the wireing, take a volt/om meter to the TPS and check things out. If you go at this willy nilly, you will never know the real problem that created this. by diagnosis this first then doing the work you will find the problem instead of just doing and hoping. Do not know if this makes sense or not. later robbie

In case its close enough situation to help, I will add that when you are testing the TPS, along with verifying that the voltage is such and such with a specific feeler gauges inserted, I also found that it is helpful to read the full range of voltages and make sure there are no "flat spots" as you slowly open and close the throttle. In other words, if I remember right, one of the tests on my TPS was fine with one of the feeler gauges inserted, BUT, as I opened the throttle from fully closed to fully open, there were several spots where the voltage just dropped down drastically instead of rising or lowering in a linear fashion. If this happens to the tps on your rig Junk, I would say the TPS is gone. Again, I'm no expert, just an amateur who worked with this problem extensively, I know how frustrating it is while you're working it out but as Robbie has mentioned, without really diagnosing this thing, its just gonna keep kickin yer arse! Another helpful hint hopefully is to take alligator clips from your voltmeter leads and clip them onto the terminals on the tps, lay the voltmeter on the intake or valve cover and just dont worry with holding the leads or the meter at all ... at first I was holding the two leads with one hand while trying to open and close the throttle with the other and that required too much coordination for me!!! Work it out man, as frustrated as you are now, you will be just as satisfied to work it out. HTH.

Thanks everyone. Will work through it.

Rick - no worries on the crank bolt. Actually, with the Thunder Gun that's the easy part