86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

Rough idle mystery

Old 12-18-2018, 04:54 AM
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In an effort to keep a good thread rolling... I've had my 91 Toyota for the last 14 years. It's a V6 4WD manual with right at 215k miles on it... For as long as I can remember, it's never idled below 1300 rpm or so and yeah it wastes some gas, but the truck has always run great and never left me stranded. It was a daily driver for year, then became a camp truck for 3 or 4 years... and I recently did a revival on it to make it a run around town, a few days a week driver again. I removed all the dents, did a color change from red to quicksand tan, new lights all around, complete new A/C system, belts, pulleys, fluids, as much as i could, you get the idea... including a new timing belt and water pump... it has zero issue doing 90 mph 3 hours each way on the interstate from my house to my hunting camp. BUT, what it does have an issue with is surging when my foot is on the brake and i'm sitting at a red light or stop sign... even applying the brakes while idling through my work's parking garage.... putting my foot on the brake makes the engine surge up to 1500, cuts and drops to 1100.

What i've tried so far is changing out every vacuum line i can locate. I've blown shop air through the coolant passage of the throttle body, i've replaced the TB intake hose, the small hose from the TB hose to the valve cover. the PCV valve, I checked the timing which was at 14 deg BTDC and set it to 10. I've also sprayed down every inch of this engine assembly with brake clean/ carb cleaner... trying to get the rpm to surge and find a vacuum leak. I've also tried adjusting the stop screws on the TB itselve to adjust the high idle, with no luck. I just saw a video where the guy adjusted something else on the TB, and i'm going to rewatch it at home and maybe do that to address the high idle.

What i'm about to try is changing the fuel filter.. and anything else you guys recommend.

I've been turning wrenches since age 5 and this truck has me scratching my head. Of course trying to find time to effectively work on it with a 1 year old pulling on my leg is also a challenge.


Last edited by bush_hog; 12-18-2018 at 05:01 AM.
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Old 12-18-2018, 07:17 AM
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Have you checked the brake booster? The fact that the idle changes when you apply the brakes suggests you could be pulling air through a leaky booster.

As far as the high idle goes, the idle speed is controlled/adjusted by the idle speed adjusting screw on the throttle body itself. It is NOT controlled by adjusting the throttle linkage or the stops on the throttle plate. I've attached the tune-up section from the FSM. The idle speed adjustment procedure is at the very end of the document.
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Old 06-08-2019, 03:32 PM
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Steve check your fuel lines

Originally Posted by Eggslinger View Post
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

check the fuel lines
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