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Discussion Starter · #1 · (Edited)
Hi everyone.

I've been having this issue with my engine for a few months: the idle constantly goes up to around 2500-3000rpm and then it drops, if I push the accelerator, I don't get any response, it slowly goes a bit higher and then drops. All of this started after I cleaned the throttle body and the IAC valve (I also replaced the gaskets for each), before that, the car was responding but it would idle at 2800-3k rpm on average.

I've tried pretty much everything I could think of and found online: bleed the coolant, changed the EGR valve, checked for vacuum leaks, got a new TPS sensor, new spark plugs, new O2 sensor; the distributor was new before this issue started, I bought a timing light and adjusted it to the time specified in the owners manual, it did run stable at around 800-1k rpm with a different timing, but I would still not get any response when accelerating, so the car can't drive; I also tested the old distributor and had the same results. I will try to clean the injectors to see if it makes a difference and clean the AFM with some contact cleaner.

After warming up the car to operating temperatures, the coolant level is still the same and my oil is clean and new, so no headgasket issues.

I did a compression test and these are the numbers I got (this was before adjusting the timing to be at around 800-1krpm):

  • Cylinder 1: 180psi
  • Cylinder 2: 180psi
  • Cylinder 3: 80psi
  • Cylinder 4: 160psi

I've been stuck with this problem for a while now and I'm getting really frustrated of not finding a solution after trying so many things, I also don't have the money to buy a new engine right now and do a swap (I'm still planning to do it in the future for a 20 valve).

Below I've attached some videos I took this month, the most recent was this week:

Most recent Idle. Stable at 800-1k rpm but no power when accelerating.
Higher and unstable idle. No power when accelerating.

Let me know if you need more videos or pictures of the car and I'll upload them.

I hope someone here can help me find a solution.

Thanks everyone.
 

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You need to check fuel pressure. Sounds like it is not getting enough fuel. It needs to be around 38-40 PSI at the fuel rail. If you deadhead the pressure gauge on the fuel line, it should be 50+ PSI.

 

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This sounds like the TPS is broken or out of adjustment. It is reporting throttle closed all the time, and that causes the fuel to cut above a certain RPM. You said that you replaced it, did you adjust it by the book when you reinstalled it? As a test, just unplug it and see if you can rev up.
 

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Let's get a better timeline on the problem, as it's hard to suss out from the original post.
It sounds like the OP had a problem with high idle and surging that prompted them to remove and clean the throttle body and idle control valve. The lack of power problem started afterward.
Idle that high is being caused by too much air getting into the engine.
A vacuum leak, a stuck idle control valve, or a stuck air conditioning idle up valve could do these things.

Did the original high idle condition start suddenly?

A possibility for a vacuum leak that big is the brake booster diaphragm; try pulling and plugging the connection in the #4 intake runner for giggle and see if it solves it. The best way to test the idle control valve is to block the ports in the throttle body. A couple layers of aluminum HVAC tape would probably hold up OK for an idle test. Block off the port labeled "Air Port to auxiliary air valve" in this picture throttle body ports by aw11mr2 . You'll need a little throttle to get it to cold start since it won't have any fast idle air. Don't get any tape under the throttle blade.

rmeller is correct about the TPS. Wiring is also in the mix, never know on these old cars. It would take a deep dive into the harness to see if there are any damaged wires that are putting signals where they shouldn't be.
 

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Discussion Starter · #6 ·
This sounds like the TPS is broken or out of adjustment. It is reporting throttle closed all the time, and that causes the fuel to cut above a certain RPM. You said that you replaced it, did you adjust it by the book when you reinstalled it? As a test, just unplug it and see if you can rev up.
Hi! Thanks for the reply. I've been a bit sick these past days, so I haven't been messing with the car.

I tried to adjust it by the book but didn't make much difference. I unplug it and the rpms start going up really fast. Here's a video:
Unplugging TPS
 

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Ok, so you have two problems. The TPS may be working properly now that you have adjusted it, and maybe not. You can always eliminate it by unplugging it. You also have a massive air leak into the intake. The throttle might be stuck open, there might be a large hose disconnected or ripped. Check everything that you touched in your previous operations, including the IAC valve. With the size of the air leak that you have, it shouldn't be hard to find.
 

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Discussion Starter · #8 ·
Let's get a better timeline on the problem, as it's hard to suss out from the original post.
It sounds like the OP had a problem with high idle and surging that prompted them to remove and clean the throttle body and idle control valve. The lack of power problem started afterward.
Idle that high is being caused by too much air getting into the engine.
A vacuum leak, a stuck idle control valve, or a stuck air conditioning idle up valve could do these things.

Did the original high idle condition start suddenly?

A possibility for a vacuum leak that big is the brake booster diaphragm; try pulling and plugging the connection in the #4 intake runner for giggle and see if it solves it. The best way to test the idle control valve is to block the ports in the throttle body. A couple layers of aluminum HVAC tape would probably hold up OK for an idle test. Block off the port labeled "Air Port to auxiliary air valve" in this picture throttle body ports by aw11mr2 . You'll need a little throttle to get it to cold start since it won't have any fast idle air. Don't get any tape under the throttle blade.

rmeller is correct about the TPS. Wiring is also in the mix, never know on these old cars. It would take a deep dive into the harness to see if there are any damaged wires that are putting signals where they shouldn't be.
Hi! The original high idle condition started after I installed a new distributor, the old one was leaking oil and I don't have the tools to disassemble and rebuild it; the car was accelerating and working though. I will try moving the brake booster connection and see if it makes a difference.

I did the test with the Idle Control Valve by blocking the Air Port to Auxiliary Air Valve with some duct tape. The idle stops going up and down for a bit and stays consistent, but high, then it starts dropping again. Here's a video:

Idle with air port blocked


Automotive lighting Automotive tire Gas Motor vehicle Auto part


I will check the wire harness; any method you recommend to check the connections?

Thanks for the help!
 

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Discussion Starter · #9 ·
Ok, so you have two problems. The TPS may be working properly now that you have adjusted it, and maybe not. You can always eliminate it by unplugging it. You also have a massive air leak into the intake. The throttle might be stuck open, there might be a large hose disconnected or ripped. Check everything that you touched in your previous operations, including the IAC valve. With the size of the air leak that you have, it shouldn't be hard to find.
Understood! I will take the time tomorrow to check for air leaks. Now I can focus on checking the hoses and finding that air leak. Thanks a lot!
 

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The best way to find an air leak is a smoke tester. Some cheap semi-pro semi-diy ones on ebay.
Most require an air compressor but I see one that just uses a foot pump.


You'll want to make sure the gaskets you replaced are properly sealed as well.
 

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Discussion Starter · #11 ·
The best way to find an air leak is a smoke tester. Some cheap semi-pro semi-diy ones on ebay.
Most require an air compressor but I see one that just uses a foot pump.


You'll want to make sure the gaskets you replaced are properly sealed as well.
I was blowing smoke with my mouth through the break booster line into the intake and checking the leaks haha. I have a small air compressor. I'll see if I can find a cheap smoke tester, because right now money is tight to be buying more tools.
 

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glass jar, an old soldering knife, aquarium air pump and tubing. consumable is baby oil soaked cotton rags. I've yet to build one myself but it seems simple enough.

 

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Wait, describe what you were doing with the brake booster line again? I meant you need to disconnect the hose from the intake manifold and then cap the manifold connection. The brake booster diaphragm can break, allowing outside air into the engine through the port in the #4 manifold runner.
It does sound like the idle air valve may be leaking through, the change from idling high to surging idle was probably the tape coming loose.

Did you use any RTV or other sealant on the throttle body and the aux air valve? I don't use gaskets there anymore, just a thin smear of gray RTV.
 

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Hi! The original high idle condition started after I installed a new distributor, the old one was leaking oil and I don't have the tools to disassemble and rebuild it; the car was accelerating and working though. I will try moving the brake booster connection and see if it makes a difference.

I did the test with the Idle Control Valve by blocking the Air Port to Auxiliary Air Valve with some duct tape. The idle stops going up and down for a bit and stays consistent, but high, then it starts dropping again. Here's a video:

Idle with air port blocked


View attachment 84131

I will check the wire harness; any method you recommend to check the connections?

Thanks for the help!
Did you set the timing properly after installing the new distributor? You’ll be chasing your tail if it’s not set properly and it will have an affect on idle.
 

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Discussion Starter · #17 ·
Hi everyone, sorry for the delay. I've been busy and haven't worked on the car.

A couple of days ago I did a smoke test and I indeed have a big vacuum leak (probably several) coming out from this weird piece attached to the intake manifold. Video attached below:

Smoke Test

I've been looking in the manual and the Toyota Parts Store trying to find what part is this. It had something that was plugging that whole but I lost that part, as it's really small and didn't know what was for. Anyone knows if it's worthy to buy or that can be sealed easily with something?

After fixing this I will do another smoke test and keep going until the car is back to normal.

Thanks again for everyone helping!

PS: the noise in the video is from the compressor running, not the car.
 

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You can cap that off with a vacuum plug. Should have one hose going to the Fuel Pressure VSV just towards the passenger side and after that there is a hose going to the fuel pressure regulator.
I still think you really need to check the timing as well
 

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Discussion Starter · #19 ·
You can cap that off with a vacuum plug. Should have one hose going to the Fuel Pressure VSV just towards the passenger side and after that there is a hose going to the fuel pressure regulator.
I still think you really need to check the timing as well
Roger that! I will check on where does that go and fix it. I used a timing light and set it to the timing that is stated in the manual. I'm going to finish fixing all of the vacumm leaks and I'll adjust the timing once again.

Thanks!
 
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