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1985 White MR2
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93 Posts
Discussion Starter · #1 · (Edited)
EDIT - Solution - Bleed coolant with new draincock.

I have read the official surging idle post which has helped greatly but I still have a few issues that just don’t make sense to me.

After fixing a couple coolant leaks my coolant system was mostly water so before it snows here in Ohio I decided to get some coolant and flush and bleed before winter. This is the root of all my problems nothing was wrong previously.
I went and got new coolant and bled it by opening the rad bleed and heater bleed and tubes etc, but importnaly i didn’t bleed from the engine bleed on therm housing because it was completely seized the plastic was stuck and I had to melt it out. I’ve seen the metal replacement part but haven’t been able to get a part #. I went to summit racing and they found an engine bleedcock with similar function, 1/4 thread with a twist valve and a spot to plug the reservoir hose. So now, this little contraption they sold me leaks when its in the open position so effectively I put more air in it then I get out, and plus my tachometer decided to go nuts today and thought it was idling out between 5k and 6k when it sounded more like 1. When I actually went to press the accelrator tach said I went to around 10k rpm I heard around 5 at most.

Note I never had a tach problem before it was always accurate, only happened when I tried to bleed it for a third time and had it connected to a trickle charger, and the surging idle only started at all once I started with the coolant job.
 

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1985 White MR2
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93 Posts
Discussion Starter · #2 ·
I have read the official surging idle post which has helped greatly but I still have a few issues that just don’t make sense to me.

After fixing a couple coolant leaks my coolant system was mostly water so before it snows here in Ohio I decided to get some coolant and flush and bleed before winter. This is the root of all my problems nothing was wrong previously.
I went and got new coolant and bled it by opening the rad bleed and heater bleed and tubes etc, but importnaly i didn’t bleed from the engine bleed on therm housing because it was completely seized the plastic was stuck and I had to melt it out. I’ve seen the metal replacement part but haven’t been able to get a part #. I went to summit racing and they found an engine bleedcock with similar function, 1/4 thread with a twist valve and a spot to plug the reservoir hose. So now, this little contraption they sold me leaks when its in the open position so effectively I put more air in it then I get out, and plus my tachometer decided to go nuts today and thought it was idling out between 5k and 6k when it sounded more like 1. When I actually went to press the accelrator tach said I went to around 10k rpm I heard around 5 at most.

Note I never had a tach problem before it was always accurate, only happened when I tried to bleed it for a third time and had it connected to a trickle charger, and the surging idle only started at all once I started with the coolant job.
To add to my list of problems the car sounds very weak to start so I’ve been charging all day which hasn’t helped and now my starter won’t even try altogether, I hear my fuel pump run but starter doesn’t try, I’m on the hunt for a missing ground but this car loves to throw me for a loop.
 

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1985 White MR2
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93 Posts
Discussion Starter · #3 · (Edited)
Ok sorted the starter issue it indeed was the battery ground on the thermostat housing, starter works great again.

I managed to find a plug for where the old one used to be with the original piece, i also connected the tube to the res and coolant and bubbles flowed, since the normal plug blocked the res tube I’ll have to think of something to stop coolant from just going right back into overflow.

The idle problem remains even after I bled all three places. Unplug tps sensor and the surging idle immediately stops. I’m sure the TPS is quite an important part so I’d rather the car not work then unplug it to drive the car, but could this mean my icv has a bubble next to it and if so how?

Tach problem is gone thankfully mustve been the weird ground making it act up, even on short drives, tps plugged in vs off only affects idle, anytime I try to mash the pedal or blip throttle it sputters and jerks until about 2k RPM then clears up, it would honestly be fine at speed limit speeds only really makes itself apparent when trying to accelerate fast. I don’t know, I suspect air still but I would have no idea how, also could someone explain the TPS and IACV more in depth I feel like my problem lies within one of those and would like to know more
 

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1987 AW11
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174 Posts
Toyota still sells an engine block drain that fits the thermostat housing perfectly. You can find it HERE, I would test the TPS and make sure the values are within acceptable ranges
Font Rectangle Parallel Pattern Art


You can take apart the dash and make sure all the connections are good, IIRC the ground strap is behind the the dash, you could probably clean it up.
 

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1985 White MR2
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Discussion Starter · #5 ·
Toyota still sells an engine block drain that fits the thermostat housing perfectly. You can find it HERE, I would test the TPS and make sure the values are within acceptable ranges View attachment 84372

You can take apart the dash and make sure all the connections are good, IIRC the ground strap is behind the the dash, you could probably clean it up.

Thankfully I won’t rip the dash apart right now because it fixed itself when the battery ground was tightened. Anyway thanks for the link I’ll wait until I can pick it up from the dealer, but do you think with a proper bleed this should fix my accel issue? I thought idle acting up made sense, but accel is also only when fully warm.
 

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... I’ll have to think of something to stop coolant from just going right back into overflow.

... Unplug tps sensor and the surging idle immediately stops...

... could this mean my icv has a bubble next to it and if so how?

... could someone explain the TPS and IACV more in depth I feel like my problem lies within one of those and would like to know more
Don't know what you are talking about here. You are going to close the valve after bleeding, right?

Disconnecting the TPS disables the fuel cut, which is what causes the zooming idle. The car will run pretty well without the TPS connected, so that makes a good diagnostic.

Most likely, although high idle from any cause will trigger the bouncing.

Search for things that I wrote. I have explained it in detail, as have others. Neither of these devices is the cause of your drivability problem. It is possible that you did some damage by trying to crank the engine with that main ground disconnected. The starter current will try to find alternate paths, and it can go places that it shouldn't. It might be a good idea to look around for burned wiring or connectors.
 

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1985 White MR2
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Discussion Starter · #7 ·
Don't know what you are talking about here. You are going to close the valve after bleeding, right?

Disconnecting the TPS disables the fuel cut, which is what causes the zooming idle. The car will run pretty well without the TPS connected, so that makes a good diagnostic.

Most likely, although high idle from any cause will trigger the bouncing.

Search for things that I wrote. I have explained it in detail, as have others. Neither of these devices is the cause of your drivability problem. It is possible that you did some damage by trying to crank the engine with that main ground disconnected. The starter current will try to find alternate paths, and it can go places that it shouldn't. It might be a good idea to look around for burned wiring or connectors.

It seems unlikely to me that the issue lies within a fuel or spark system, have it be an electrical problem or not, I’m not saying it’s impossible and will look for burned connections but the ground wasn’t disconnected it was connected weakly not tight enough, it cranked slow at first then not at all.

Aside from that my accel issue only happens when it’s at operating temp so I’m thinking it has to be something to do with the flush I recently did. How can I troubleshoot further? The correct part to correctly bleed it is on the way but in the meantime what are some things I can cross off?
 

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The flush itself has nothing to do with the drivability problem. Something that you broke while you were doing it might. Check everything that you touched, and everything that was nearby.

The problem with the starter ground is that the starter draws hundreds of amperes, and that current is going to find another way to get back to the battery. People have reported their speedo cables or handbrake cables smoking. So, there may be small auxiliary ground wires that have burned up, and if one of them is a ground for engine controls, then that could be what is going on. So, inspect all around the engine and ECU for little brown wires that look like they had a hard time.
 

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1985 White MR2
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Discussion Starter · #9 ·
The flush itself has nothing to do with the drivability problem. Something that you broke while you were doing it might. Check everything that you touched, and everything that was nearby.

The problem with the starter ground is that the starter draws hundreds of amperes, and that current is going to find another way to get back to the battery. People have reported their speedo cables or handbrake cables smoking. So, there may be small auxiliary ground wires that have burned up, and if one of them is a ground for engine controls, then that could be what is going on. So, inspect all around the engine and ECU for little brown wires that look like they had a hard time.

Ok, I'll start from there. I found something that did seem like it could be damage I did but I am unsure if it is causing the driveability problem. On the thermostat housing there are two blue vacuum switches with two holes each connected to the metal vacuum lines, anyway, from what I've found that's evap and fuel, and the crankcase vent switch. Well either way I cannot distinguish them but one of them is broken. I must've damaged it when pulling out the vacuum lines from it because they were very very tight. It looks easily fixable like something some plastic welding could fix. Could this cause my driveability issue? What about the inconsistent idle?
 

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1985 White MR2
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Discussion Starter · #10 ·
The flush itself has nothing to do with the drivability problem. Something that you broke while you were doing it might. Check everything that you touched, and everything that was nearby.

The problem with the starter ground is that the starter draws hundreds of amperes, and that current is going to find another way to get back to the battery. People have reported their speedo cables or handbrake cables smoking. So, there may be small auxiliary ground wires that have burned up, and if one of them is a ground for engine controls, then that could be what is going on. So, inspect all around the engine and ECU for little brown wires that look like they had a hard time.
Low and behold I found some damage that looked like it had been from heat and smoldering. The harness beside the fuel rail was a little charred between cylinder 3 and 4,I stripped it back and found nothing no damage it was prestine and I found some work done by someone else, three brown wires spliced together. I didn’t know the car had any past service so definitely interesting. I will continue to look around for more damage but everything checks out right now.
 

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Low and behold I found some damage that looked like it had been from heat and smoldering. The harness beside the fuel rail was a little charred between cylinder 3 and 4,I stripped it back and found nothing no damage it was prestine and I found some work done by someone else, three brown wires spliced together. I didn’t know the car had any past service so definitely interesting. I will continue to look around for more damage but everything checks out right now.
Toyota splices many of the harness wires so that isn't out of the norm to find them. They are usually just grounds and battery + wires.
 

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1985 White MR2
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Discussion Starter · #12 ·
Solution - Air in coolant

The surging idle remained with everything I tried to fix but eventually the toyota part came, I went today to pick itup and installed it with 0 issues. I easily bled the large amount of air out of both my radiator and thermostat housing. After which my car idles better than it did before and I was able to set the screw around 900 RPM stable, I still have an uncapped vacuum line so makes sense.

Anyway I thought it was also worth noting that rmeller was correct, the starter ground caused my injectors grounds to smolder and loosen from the solder I had applied from a previous repair. After resoldering and tightening the battery terminals (was very picky about tightness or else injectors wouldn’t fire.) But all in all everything is working now thankfully, and my acceleration and surging idle problem are a thing of the past. Wondering in hindsight if the accel problem was due to smoldered injector grounds or air in coolant?
 
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