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Rough idle mystery

Old 07-09-2015, 06:07 PM
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Rough idle mystery

Hi, I'm new here to the forums and also new to Toyota ownership. I got a great deal on an '89 V6 with just under 54k miles. Before I go any further, i might (should?) sound like I hate my "new" truck; I don't... I love this thing. But she needs help.

I took it to have an oil leak checked out and fixed and since it was there, I went ahead and had the spark plugs and distributor cap done, oil changed, engine air filter replaced, and trans fluid changed.

So, when I went to pick it up a problem developed. It doesn't idle right and to make a long story short, the shop took an extra entire day (on them) trying to figure it out. Let me back track a little. When I brought it home, I got off the exit to my home and experienced what I thought at the time was something brake related, now I realize what I was feeling was this low choppy idle just before coming to a complete stop ( it didn't do that again until after the service and at the same time, it went below 1/4 tank so I'm thinking it sat a lot instead of what the previous owner told me).

With my permission, they took off what appeared to them as the original fuel filter and said it was nasty. They think because of that and because of the smell, bad things are in my fuel tank. For now, they suggested filling it up with gas and adding seafoam. I did that.

I drove it today around ten miles and did not notice any change. It idles rough at a stop, struggles a bit to get going, but once under way, it drives fine.

They suggest as a next step cleaning or replacing the fuel tank and fuel strainer. I don't feel like I'm being scammed but then again the cost continues to rise!

I was wondering if you guys think this is the next step to take, if there is something else that should be checked out first, and also, if you think I should give the seafoam more time to do its thing (I've never used it before and am not sure if it should be done with several tanks of gas to clear up a severe problem)

Thanks in advance for the advice

Steve
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Old 07-09-2015, 10:01 PM
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This could be a number of things. New truck require a fresh service. Check all vacuum lines. Since filter was filthy, put some fuel cleaner in the tank (seafoam or Barry's). Check idle and timing, fuel quality, plug wires, etc. It's probably something very simple, I would not jump into big projects like tank cleaning.
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Old 07-10-2015, 01:18 PM
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You may want to clean out the fuel tank. I did the seafoam treatment on my gas tank after the truck sat for 10 years. There was 3 or 4 inches of sludge on the bottom of the tank. It certainly cleaned it up, but there was so much crap left over that it would ruin any fuel I put in there and it clogged 3 filters. The gas was still brown after 3 fill ups. I removed the tank, made sure it was squeaky clean, put it back on, and haven't had a problem since. Save yourself some money and do it yourself. It's not a difficult job, just dirty. I did it in a afternoon. Just be careful when removing the fuel lines on the top of the tank, its really easy to snap off the fittings because they're usually rusted. It happened to me...

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Old 07-14-2015, 06:34 AM
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Noahstancik,

I wish I could do it myself but I recently moved into an apartment and car work is not allowed. That's why I'm trying to figure out what do have done next- expense! I have to question the dirty fuel thing, I mean, I'm sure it's an issue but maybe not THE issue. It seems logical to me that since they changed the fuel filter that it shouldn't be this bad if I immediately filled the tank with high octane and added sea foam...seems like it would become progressively worse over time.

I have noticed in the last couple of days that after a cold start it runs fine but gets rough quick. After all I've read, it sure seems like a vacuum problem, I'm thinking maybe I should get a torch and go park on a dirt road and test the vacuum hoses since they couldn't finalize a fuel tank quote but guessed around $400.
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Old 07-14-2015, 06:57 AM
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I would remove and take a close look at the air intake hose. They are prone to crack in the ribs and on the bottom area where it is hard to see. Any leak between the throttle body and the AFM will cause idle problems.
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Old 07-14-2015, 07:03 AM
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After I put the new fuel filter on the truck ran better for a few miles, but went back to running rough. Putting more seafoam in there would just disolve more of the gunk inside the tank. You would have to go through several fill ups before your fuel came out clean. When I cleaned out my tank, I actually found gravel. Don't know how it got in there...
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Old 07-14-2015, 07:48 AM
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Noahstancik,
Gravel? That's crazy! I filled it up yesterday and threw in some techron since everyone has an opinion about these products and it seems there are more techron lovers than sea foam. It's good to know it'll take several fill ups for it to improve--well, I guess. The way I figure it, if does start to improve, that means it is the fuel tank and the cost of cleaning/ replacing!

Offroadnutz,
Thanks! I'll check that out and hopefully it'll save the tank clean/change

I know you guys do your own work and like I said, I can't. So Would it be wrong or insulting to suggest they check out vacuum hoses before they get into the fuel tank? From what I've found researching this issue, vacuum line problems seem to be a definite possibility and yet, according to my receipts, I don't think they were checked. Or, would issues with them show up on computer analysis or something?
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Old 07-14-2015, 07:49 AM
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how was it running before any repairs were done? what oil leak did they fix, the valve covers? i hate to bash on a shop without knowing all the details, but you may want to pony up and have a more qualified shop properly diagnose the real problem before they throw more parts at it.
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Old 07-14-2015, 08:04 AM
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Hi oldblue,

It seemed to be running fine when I bought it and when exiting the interstate and coming to a stop down the ramp the breaks felt like they may have an issue. What I now think I was feeling is the beginnings of that rough idle. I took it to the shop the following morning with no idle problems but the shop is about 1.5 mi away. Yes it was a valve cover gasket.

I talked to another shop and of course they have the initial cost of diagnosis. So, it's like starting over lol. I'm new to this area (and state) and so, I don't really know anyone who can give me the name of a good mechanic....I'm screwed!
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Old 07-14-2015, 08:09 AM
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If it runs fine at high speeds but idles rough, fuel flow problems would not be my first suspect. Generally a blocked fuel filter or plugged line will give you the opposite results - able to supply adequate fuel for idle, but not for full power operation. Same thing with ignition problems - they usually show up first at higher power operation where cylinder pressures are higher creating higher voltage requirements to fire the plugs.

First, make sure the check engine light works (it should come on when you turn the key on before you start it) so you can check for diagnostic codes. If it's not working fix that and check for codes.

Beyond that, as has been mentioned, start with the integrity of the air supply to the engine, and also check thoroughly for vacuum leaks. An unlit propane torch held near the various potential leak areas while the engine is idling will help spot leaks. (The engine will speed up when it draws in the propane). You can also make a simple stethoscope with a piece of hose held up to your ear. Vacuum leaks will be apparent when the other end of the hose gets close. Just keep the hose out of the fan belt.

- Make sure the distributor timing is set correctly.
- Make sure the TPS (throttle position sensor) is healthy and properly adjusted. The FSM (sticky links at the top of this forum) has procedures for checking it. In particular, if the TPS idle switch isn't closing properly, the ECU won't know your foot is off the accelerator and it will try to manage the engine as though it was in cruise, causing a tendency for surging at idle.
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Old 07-14-2015, 09:19 AM
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Originally Posted by Eggslinger View Post
Noahstancik,

I wish I could do it myself but I recently moved into an apartment and car work is not allowed. That's why I'm trying to figure out what do have done next- expense! I have to question the dirty fuel thing, I mean, I'm sure it's an issue but maybe not THE issue. It seems logical to me that since they changed the fuel filter that it shouldn't be this bad if I immediately filled the tank with high octane and added sea foam...seems like it would become progressively worse over time.

I have noticed in the last couple of days that after a cold start it runs fine but gets rough quick. After all I've read, it sure seems like a vacuum problem, I'm thinking maybe I should get a torch and go park on a dirt road and test the vacuum hoses since they couldn't finalize a fuel tank quote but guessed around $400.
Originally Posted by RJR View Post
If it runs fine at high speeds but idles rough, fuel flow problems would not be my first suspect. Generally a blocked fuel filter or plugged line will give you the opposite results - able to supply adequate fuel for idle, but not for full power operation. Same thing with ignition problems - they usually show up first at higher power operation where cylinder pressures are higher creating higher voltage requirements to fire the plugs.

First, make sure the check engine light works (it should come on when you turn the key on before you start it) so you can check for diagnostic codes. If it's not working fix that and check for codes.

Beyond that, as has been mentioned, start with the integrity of the air supply to the engine, and also check thoroughly for vacuum leaks. An unlit propane torch held near the various potential leak areas while the engine is idling will help spot leaks. (The engine will speed up when it draws in the propane). You can also make a simple stethoscope with a piece of hose held up to your ear. Vacuum leaks will be apparent when the other end of the hose gets close. Just keep the hose out of the fan belt.

- Make sure the distributor timing is set correctly.
- Make sure the TPS (throttle position sensor) is healthy and properly adjusted. The FSM (sticky links at the top of this forum) has procedures for checking it. In particular, if the TPS idle switch isn't closing properly, the ECU won't know your foot is off the accelerator and it will try to manage the engine as though it was in cruise, causing a tendency for surging at idle.
Have you cleaned your throttle body lately? A dirty throttle body can cause a rough idle as well. Best think would be to get some throttle body cleaner from OReilly's or AutoZone and just spray the plate and wipe with a paper towel. That should improve your idle somewhat.
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Old 07-14-2015, 09:09 PM
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Wow, this great information, thanks so much. I'll let you guys know what I find once I figure out where I can do the work. I guess I'll just work out on the main road off apartment grounds lol
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Old 07-14-2015, 09:26 PM
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Originally Posted by Eggslinger View Post
... I guess I'll just work out on the main road off apartment grounds lol
Didn't your mom use to tell you to go play in the street anyway?
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Old 07-15-2015, 08:29 AM
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Originally Posted by RJR View Post
Didn't your mom use to tell you to go play in the street anyway?
LOL yep, and said don't come back till the street lights come on.
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Old 11-27-2015, 06:23 PM
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Try cleaning the fuel tank. Sea foam is wonderful stuff
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Old 11-27-2015, 06:36 PM
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Smile

Originally Posted by Eggslinger View Post
Noahstancik,

I wish I could do it myself but I recently moved into an apartment and car work is not allowed..
Oh it can be done you just have to do it after the office closes and on the weekend. I kept my tools in the apartment and only took out
what i needed. Granted my apartment looked like i was losing a game of Jumanji. But the wife put up with it and I did a head gasket and timing chain job on a 1986 Sr5.

Last edited by Obmi; 11-27-2015 at 06:37 PM.
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Old 01-19-2016, 08:20 PM
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Any luck yet? If not it could be the knock sensor or wiring harness. Mine was doing the exact same thing. Swapped er out and fixed the problem.
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Old 01-18-2017, 06:03 PM
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Bad idle/black smoke fix for carbed 22r

If your truck is idling horrible when cold and blows black smoke buy a rebuild kit for the carb. 36 bucks at O'Reilly's. It's the auxiliary accelerator diaphragm. If you pull the vac line on the bottom driver side of the carb and have gas in it that's your problem. Changed eveverything out that was in the kit and it's like a new truck. Automatic Choke started working again too

Last edited by Jake Houts; 01-18-2017 at 06:05 PM.
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Old 09-30-2018, 10:45 AM
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I know this thread is old, but I wish people would post their solutions!

Eggslinger, did you ever fix your issue? Did you sell the truck and say, "To Hell with it?!" It seems that people either fix and forget the thread, or they move on.
I have a similar issue.
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Old 10-03-2018, 04:06 PM
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I bought a 93 Toyota RV which had sat a long time. Went through and replaced everything.

The fuel filter was bad nasty, surprised any fuel was getting through it. Not being a motor head or mechanic I did not think to ask the question, "where is all that nasty stuff coming from" or maybe I was in denial and did not want to know.

Bingo, inside the fuel tank. When the pump went out dropped the tank and it is nasty in there. Not sure if the pump failed or the sock was so plugged that fuel would not go through it!
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