Scott Baxla

I've got a 95 T100, 3.4L and it is difficult to start when its up to temp - somewhere around 30 minuted after shutting off. It appears to be fuel starved because it starts with starting fluid. It also runs a little rough when it first starts in these circumstances. No hitches when starting it cold. Mechanics find air being pushed through line instead of fuel. The fuel pump has been replaced twice in the last 4 years due to this problem, last time w/ OEM. Suggests its not fuel pump. Seems like the pump would either work or not work and that the issue would be worn impeller, which is doubtful a pump less than 3 years old. (2nd replacement happen after 2 years on first replacement.) What other components could be a part of this issue? One mechanic called the bracket holding the fuel pump a "sending unit"? And there is a fuel pump relay? Temperature related? (assuming it gets a little hotter than operating temp when shut down and shutting cooling system down.)

ksti

First thing I would check is the IAC valve to see if it's clogged up.

wyoming9

iTrader: (1)

Leaky injectors fouling the plugs

If this starts fine after it sits all night

It fires on starting fluid because it is more volatile then gas and there is enough spark to light it off

Just how is this air in the fuel line being detected ?

Air in the line would mean your sucking air unless your driving around on fumes with the fuel level so low the pump intake is sucking air

Which would happen even when it sat over night

Scott Baxla

Plugs aren't fowled, and its happening when the engine is up to temp, not when sitting over night. I've inquired about injectors, and its been declined. How do you test injectors anyway? (The truck is over 20 years old, 440K miles, and I'm pretty sure they've never even been cleaned other than running sea foam through fuel once at time of a cat code.) One mechanic touted the brand of injectors that toyota used in these trucks as being bullet proof, and if I were to change them on a whim, I'd be replacing a quality part with an inferior one, or paying through the nose... He felt like they weren’t showing any signs of being the issue, and ruled them out. (I've probably had at least 8 different mechanics trying to resolve "these" issues on my truck in the past 4 years, including toyota, and they have all surrendered - can't find it.) I originally thought it was acting flooded, but the current mechanic was getting it to start w/ starting fluid. (I thought flooded because I’d pump gas pedal to get it start, then run really rough at first w/ poor emissions after start) As a test, current mechanic is having me cycle the ignition key on and off a few times for a couple of seconds when it gives me the problem. Theory being that the fuel pump turns on for a second when you first turn the key, and by doing the cycle it will give it enough gas to start, and then the vacuum takes over. That much seems to be confirming his theory. His theory was that the fuel pump impeller was bad and it was cavitating and sending air into the line. The fuel pump has been replaced twice in the last 4 years by a different mechanic - under the same theory. Previously, the first mechanic was thinking that the first aftermarket fuel pump was bad and we went to OEM for the 2nd one and now current mechanic is finding same issue. Seems unlikely that the fuel pump is the issue to me at this point. Toyota dealer told the current mechanic that they've probably sold “one” of these fuel pumps in the last 20 years - i.e. they don't go bad. (probably not quite accurate info, since I know they sold one to me – the only one???) This new mechanic also suspected fuel sensor (gauge) was inaccurate and the tank was dreadfully low on fuel - i.e. access to air to pump from dreadfully low fuel level. He added a couple of gallons of gas, without resolution. (the tank had about 15 gal in it - not low on gas at all – can’t imagine there is any air to pump under 15 gal of fuel). The current mechanic says the "bracket" supporting the fuel pump is some sort of a fuel sending unit. He's finding the air by pulling the line off of a filter and its pushing air instead of gas. Don’t know where he’s pulling the line. I can’t imagine where air would be coming from (we’d smell gas if there was a leak in line admitting air.) Fuel draining back to tank after shut down, leaving air in line? 20 years or so ago before computers and OBD, I remember "vapor lock" as being an issue on some vehicles - don't know if it would be somehow related to this... The current mechanic had an advantage in that the "inconsistent problem" had escalated and was happening every time so he had a window to try things. He did a thorough smoke test and found a hidden vacuum line on the back of the intake disconnected. Now w/ line connected, the problem is no longer consistent (and that vacuum line has likely been disconnected for quite a while, so why did it all the sudden escalate?) He also added ½ gal of coolant to radiator and wonders if it was part of the solution: 2 gal of gas, ½ gal of coolant, connect vacuum line. I suspect it was the improvement was wholly due to vacuum line. Poor emissions was on the problem list, and they seem to be somewhat better w/ line connected.

It has been idling high, and is now idling even higher.(with vacuum line connected) and still running a little rough in idle at start up. The fuel mileage has been down - a bit sporadically down or more accurately, down but sometimes down significantly more. Now after attaching vacuum line, fuel mileage is way down (and idling higher…) Previous to this recent escalation, the check engine light was coming on sporatically - 95% of time the code is "Throttle position sensor", occasionally some lean / bank 1 code. W/ escalation it was coming on consisently - every time it was cleared, come right back on when the current mechanic was testing it. It stayed off for a week after vacuum line attached, but just came on again - not sure yet what the code is. I've read other threads about idle air control valve after Ksti suggested checking it. Many reported it resolving idle and fuel consumption issues. The part is on its way to me. I'd rather clean the OEM part that's on truck, but it seems wise to have the part on hand in case the IAC tests bad (12 v across terminals turns valve in each direction and doesn't arc in iac motor). I know the idle is not right and it seems this is the only part that affects idle, so the current direction is to go after this likely culprit and see if it knocks out some other symptoms.

Other parts that have been replaced in this ghost chase (without results):
-TPS replaced twice, second time w/ OEM.
- Breather snorkle replaced (it had a crack in it - vacuum leak)
- Mass air flow cleaned.
- Mass air flow replaced.
- Throttle body cleaned by 2 mechanics - don’t know if they took it off of truck to clean (more crap potentially drained down into IAC port), and almost certain they did not clean the attached IAC since they did not say they did.
- Wiring connector to TPS replaced - could get engine to skip by wiggling connector (Skip feels like fuel/no fuel to me rather than a firing skip). This “skip” is one of the symptoms and it sometimes happens while driving down highway, and sometimes while accelerating. Haven’t noticed it yet in the week since vac line attached.
- Temp sending unit replaced (one that communicates w/ computer)
The mechanic that chased this thread says helper saw the OBD reader go from reading normal temp after shut off to some negative temp (when I was thinking it was acting flooded, it made sense.)
- Computer (the only other component that would be a part of a sudden neg temp read?)
- Down stream O2 sensor. (suspected a few times due to the bank 1 code?) Seemed to run a little better for a few days at least, then the escalation happened. The nuts holding it on were all but gone – any contribution due to -O2 could have been an air leak and not the sensor itself?
- Catalytic converter (it was actually showing a code for the cat at the time - probably the only legitimate part replaced).

Seems like IAC and fuel injectors are only parts left, other than EFI fuse link/wiring)…

RASALIBRE

Scott Baxla

Did not clean IAC valve and chose to just install new aftermarket IAC (from Taiwan) - mechanic was complaining about me wanting to clean the old one. Idle got even worse w/ new part- now idling over 2K. And restart after 30 minutes issue got more consistent. Running RPM at low speeds is close to 1, and now (this seems like a new twist) when I approach a stop light, the engine oscilates/pulses between 2K and 1K - its confused if its running or idling until I get to a complete stop and its stays at over 2. and drops again when I start moving. I kept the original IAC because its OEM, and it was quite carboned up. I took it to my small engine repair guy who has a sonic bath for cleaning carburetors, and he dissassembled the IAC, soaked the appropriate part in the bath and the thing is spiffy clean now, and ready to reinstall. Since the new IAC made the problem worse, I'm assuming that IAC could be on the right track. The small engine repair guy works on his own vehicles, but not for hire (something about insurance or license), so he can't work on my truck. He did say that with small engine repair, he uses aftermarket parts all the time, but not for carburetor components or electronic components, and he thought the aftermarket IAC was not a good idea. (a new one from Toyota is $400, aftermarket from Auto Zone $200, This one came from ebay directly from Taiwan for $40, and took a month to arrive, $150 labor to install.) Some other threads have suggested the throttle body could be an issue - particularly a worn butterfly shaft inside it, and some say something about lubing it with some sort of special lube. Is it supposed to be lubed & the cleanings have removed it? / with 440K miles, it couldn't possibly have any lube left on it if it started out with some... The current mechanic says Throttle body is either physically broken or it works (if clean and shaft moves butterfly freely) and its been cleaned 3 times now. The current mechanic was also able to push on the TPS (toward the shaft in throttle body that its attached to) and the idle would change, release it and it would change back. He thinks the TPS is bad and wants to replace it. I'm skeptical, and think it might have more to do with the shaft inside the throttle body? TPS has been replaced 3 times now without results, and the current TPS is OEM. My current plan is to reinstall the old IAC (now clean and looking new inside) and while doing that, have the throttle body thoroughly cleaned while off the truck and ask about a close inspection of the shaft to see if its operating freely. I could get a used throttle body for $250 supposedly with less than 200k miles on it (mine has 440K), but if its true that its either physically broken or it works...? Have not tried anything with fuel injectors yet. Can tell current mechanic is tired of this and he's said he doesn't know what the problem is. I'm going to my Dad's in a couple of weeks and will get his mechanic to reinstall the original iac, etc. Then ask him his thoughts about replacing throttle body or fuel injectors if IAC doesn't do it. Years ago when I got the first TPS code I was there and he said it could be IAC. Any thoughts out there?

WolfMann

I would say check your battery/charging system, maybe clean up your grounds, and take a look for any funky wiring. You checked the fuses right? Electrical gremlins can cause emissions issues. I was also going to suggest mass airflow and throttle position but it sounds like you've looked at those. Replacing tps instead of cleaning might be a good test. Fuel/air filter? Vacuum leaks? Timing? Probably stuff you've already checked but it's good to go over the little things first.

Co_94_PU

iTrader: (-1)

I didn't read all.of this (forewarning)..

If pressing on the tps has any effect it is not properly cinched down fully (moving the throttle plate) or "wet' allowing the signal level to change due to the " signal to ground, voltage) or a bad connection.

I agree you have a sloppy throttle body, specifically the rod the throttle plate rides on has worn down. The only solution there is a expensive overhaul with machine work and a sleeve or "NOS".

Scott Baxla

CO 94 PU: Thanks for your comments. Didn't consider overhauling the throttle body w/ machine work. Does sound expensive, and a lot of time without a truck while its done. Might see where the IAC and a thorough throttle body cleaning goes first, but will press Dad's mechanic for his opinion when he has it off and in his hands. Not sure what your comments were about the TPS ("wet" or "NOS" for Throttle Body), but sounds like you're suggesting something's not right. I'm pretty sure TPS will at least come off for inspection when the throttle body comes off to replace the IAC.

Wolfmann: Thanks for your comments too. This has been going on for for maybe 3 or 4 years now and getting worse. During that time all the little stuff you''ve mentioned has been checked many times, and many parts replaced without effect. Electrical looks sound as much as can be seen, and connections look good, although it would make sense that an electrical issue could be involved. A new, theoretically unrelated issue has cropped up recently: Dash lights, and tail lights are out, and the replaced fuse blew right away, so there is a short somewhere in that wiring. Don't know if it happened at the same time, but the aftermarket cruise control quit working and I'm suspecting that maybe the power feed for that is in the same circuit, and maybe even the cause of the circuit issue, but I don't know how the cruise is wired in. (inspection of rear lighting wires was uneventful and haven't taken the dash apart yet. The TPS codes started years ago though and the lighting issue is fairly recent The TPS has been replaced 3 times, last time w/ OEM, all without effect. The problem has escalated to this pulsing tach when coming to a stop, so it appears to be worse than ever. You would go for the TPS again?

That's 2 comments and the current mechanic's opinion that maybe the TPS actually is causing a problem right now. I'm sure the IAC is not right too though since the idle RPM increased by about 500 when the current one was installed.

Scott Baxla

5/9/18 update: As suspected, the electrical issues w/ dash lights and tail lights were unrelated to the idle and starting issues.

IAC was definately part of the problem, and cleaning it was the fix for that - not replacing it. KSTI nailed that one right off the bat.
I had first tried replacing the IAC Valve with a new taiwan part, and it made the idle worse. I had my dad's mechanic in Florida put the old IAC valve back on (cleaned in sonic bath by my small equipment repair guy). The idle can now go back down to around 1000 which is were it used to idle, but when I come to a stop while driving the idle is still pretty high until I punch the accelerator, so it seems to be pretty certain that there is wear on the rod in the throttle body that is causing it to stick. New throttle bodies are not available for this engine. I found a used one with 150K miles on the motor for $250, (my motor has 450K). Are there other 3.4L motors whose Throttle Body would work? I've seen a few threads somewhere about adding a helper spring to the throttle body or doing some sort of special lube in the throttle body? The Throttle body has been cleaned a few times. (it was not sticking before it was cleaned...maybe the crud built up on the rod had honed itself to a smooth fit?) I'm now back in North Carolina, and the mechanic I'm trying to get to work with me on the starting issue said something about sending the throttle body through a sonic bath. Anything in there that would get damaged by that? (the IAC valve had to be dissassembled to remove the electrical parts before the bath, but the small equipment guy did a good job with it.) And I've learned all sonic baths are not the same. The small equipment guy has one of the good ones for cleaning small equipment carbs. I've heard there are others that are pretty much not worth the time. Anyway, the small equipment guy is no longer available, at least "until further notice" - he's had to go back home to Canada because of something to do with his parent's health.

CO 94 PU: you mentioned an expensive overhaul of the throttle body - sounds like some sort of filling in of the holes that the rod goes through and reboring them to the proper spec and replacing the rod? Are there specs somewhere on what the size of the hole and rod are supposed to be (or the difference/clearance between them)? What is an "NOS?

The TPS check engine light has not been coming on since the original IAC valve was put back in a month or so ago. So far so good on that element.) However, its still doing the "fuel starved when hot" thing at about 30 minutes after shut down. Any chance that only fixing the throttle body sticking would change the starting issue? - maybe just off enough at that temperature that the computer is saying don't send gas?) Wyoming 9 suggested leaky fuel injectors (and I've heard a few other comments about the possibility of fuel injectors being part of this issue - maybe even a wiring short to the injectors). What is not making sense is that it happens at about 30 minutes after shut down (I'd guess that's about peak temperature since the motor has heat, and shutting it off shuts off the cooling system?) It does not happen at 15 minutes, and it does not happen at 45 minutes, only if I go into a store and take about 30 minutes and come out to try to start the truck. I can often get it started anyway, by cycling the key off several times (someone said it turns the fuel pump on for a second or so each time it's turned on) and then pumping the pedal a bunch while starting, and it will sputter into a run and then run great. On one or 2 occasions, (both in Fla - 95 degrees parked in full sun parking lot) I had to spray starting fluid into filter box, and then it cranks up right away, and runs fine. The truck in general is tough on starters (maybe 3 in the 250,000 that I've owned the truck) and this starting problem I'm sure is also wearing the starter.