code 51/ quits when returning to idle

[professorbob]

1989 Turbo Targa with automatic transmission. After transmission rebuild and reinstall of engine and transmission, (See other post) the car ran great for 125 miles. Then suddendly at about 70mph started balking and dropped into limp home mode. Initial symptoms indicated possible bad fuel pump. Fuel pump replaced. and No joy....
The intake horn was cleaned during engine refresh of blow-by oil. Because the Turbo uses a Vortex generator, this UNIT SHOULD NEVER BE CLEANED as damage will occur. (Dealer price 700.00) Purchase a used replacement electronics on Ebay. Still not joy. This unit had the black sealer so it was not from a 1989 year car.
Found a local Supra owner who removed his good electronic meter and installed it. The performance improved by still not out of limp home mode. The new valve cover gaskets were leaking because the screw had worked loose. Tightening the gasket screws seems to help the problem. Have removed the Idle Air Control and Throttle Position Sensor for trouble shooting. Will now have to replace the large hose as it broke upon removal. Anyone have a source for pre formed hoses other than the dealer?
Are the IAC and TPS available as aftermarket parts?
All ideas and suggestions are welcome.

[cre]

Every condition which would cause "Limp Mode" should record a code in the ECU or the ECT. Code 52 is the only one that's commonly seen on these cars. The TPS and ISCV will NOT cause the car to go into limp mode, just idle issues and poor throttle transition response. Code 51 only mean that the A/C is on or there's a problem in that circuit OR The throttle is open or there's a problem with the idle switch (IDL) in the TPS.... if you're on the throttle or have the A/C on the code will show up but will clear a few seconds after you get off the throttle or turn off the A/C. Note that you cannot set ignition timing with code 51 (or any other code) present and you MUST make sure to install the diagnostic jumper when doing so. Is the ECT light on or flashing? Any code 52?

[professorbob]

Car still operating rich and will not shift out of second gear and engine is being held to less than 2,000 under driving load.
Checked the Throttle Position Sensor TPS and it checks OK. Idle Control Valve ICV is carbonized and used some cleaner on the plunger. Is the plunger suppose to close completely? I can suck air through the port even when closed.
Any sources for replacement parts other than dealer.
The A/C is no longer cooling. It performed well for the time the vehicle was working. I had added a can of freeze 12 then. Non only warm air. Maybe this is the reason for the code 51.

I am looking for a safe way to check the vacuum hose joints. Suggestions. Someone suggested pressurizing the vacuum system at the hose from the carbon canister and applying bubble soap.
Still looking for source for form hoses. Any suggestions are appreciated.
So want to get back in the road again.
Is there a standard reason for tripping into limp home mode?
Thanks
Prof.

[professorbob]

Still trying to get the supra back on line... Finally have an inside area with heat to do the work. Update. Car ran great for 120 miles then started cutting out and now will not operate above 2000. I have lost the gasket between the manifold and header I installed new when the engine went back in.
After some effort of multiple tries and seeming more fuel being added with each try the engine will start and seem to go through the normal warm up as required. I suspect that the difficult start is fouled plugs. As the normal operating temp is reached and rpm come back the engine goes through occasional hesitation. I can apply throttle until about 2300 rpm when it acts as though the ignition has been momentarily stopped until it goes back to idle speed. There is a very rich condition and soot is blowing out around the header. I have a replacement gasket ordered.
Can a clogged converter cause enough back pressure to cause a gasket blowout and these issues. The rear exhaust seem to be normal.
If so is there a way to determine converter condition without removing the exhaust again.
What about a bad O2 sensor as the one on the turbo housing. IF it is bad will that create these issues?
All suggestions are appreciated.

I am going to check codes, but expect that I have not been able to operate the engine long enough for the on board diagnostics OBD to make a check.

[cre]

A clogged cat is a possibility, especially after a rebuild. I'd test the AFM first. You haven't sprayed the AFM out with any water or cleaners I hope. Also, if you have any error codes present you cannot set the ignition timing... This may account for part of the problematic behavior.

No, a bad O2 sensor will not affect your fuel mixture to this degree. The ECU does not even use the O2 sensor until the vehicle is up to normal operating temps.

Clear any existing codes and see if any new ones are set. Some codes may show immediately if there is a problem with a component such as 24, 31, 41, 51, 52 (these are the more common error codes); A lean condition or rich condition or O2 sensor fault code will not show up until the vehicle is up to operating temp and has been driven. Depending on what the defect is some codes may show up right away or not until later such as AFM related codes like 24 and 31; So if you don't see these right away don't dismiss the AFM as a suspect.

[professorbob]

Thanks Cre for the rapid response. As you can gather, these issues have been ongoing for over 6 months.... See previous post for updates... I actually replaced the AFM module with a used unit, because I too had no clue that cleaning the module would kill it.
Thought originally that that is why the car started these issues after 120 miles, because the new replacement was used, borrowed a functional unit to determine if that is the issue. Very little improvement. Do you know of anyone I may send my unit too for a proper diagnositic of the modules.

This most recent problem with the blow gasket is what makes me believe there is a restriction in the converter. Just do not know how much restriction is required to cause the gasket to blow.
Is there an effective way to determine it the turbo is operating properly. I understand that it lays out unless the vehicle is driven.
My turbo needle is below 0 on the boost gauge.


The gasket arrive just now and I will be jacking the vehicle to remove the header for reinstallation.

[cre]

It's going to be loud as hell, but pull off the cat and take it for a quick spin around the block.

[professorbob]

When I separate the header, a road test may not be necessary. If there is a backup, the relieved pressure may very well allow me to do Wide Open Throttle WOT test without the cut back to idle. If it does then I will have solved a months long mystery. Keeping my fingers crossed. I will post what I find out.
Thanks
For the help.
Prof.

[professorbob]

Dropped the header just enough to ease out the gasket. Did not seem to be crushed.. Starter the car and let it warm a few minutes.
The engine did not start instantly. It required about four tries. Each time I move the switch back to off and waited a second. Each time the attempt to start was better until it kicked off.
It immediately went into warmup mode and after a few minutes dropped back to the normal idle position.
Each time I would accelerate through about 2200 rpm the engine would stop and allow rpm to drop about half before increasing again. Holding the accelerator at the same position would cause the increase and stop again and again.
Very rich condition exist with huge amounts of black smoke coming out the header. I do not believe that there is anything wrong with the exhaust system.
I do wonder about the gasket thickness in that it does not seem to be able to keep the tube from the down pipe sealed when it is bolted up against the header. Just wonder is there is one slightly thicker to stop the leakage. However, the one just removed was installed new at the last install.
Would the be considered a fail safe mode? If so what conditions exist to cause the computer to create this condition.
Would the transmission inputs cause this?
What about the fuel pressure regulation?
Am quite frustrated with not being able to determine what is causing this issue.
Finally I have a slight amount antifreeze dripping down the back side of the block. Just wonder how to make sure the hoses are tight enough.

Any help is appreciated.
Prof.

[cre]

Put the car in diagnostic mode and run it. Watch for any codes (other than 51 which you'll set from pressing the throttle). It does sound quite a bit like limp mode. I can't think of anything pertaining to the transmission that would cause the car to respond like this, especially while stopped. It requires a significant problem for the ECU to enter limp mode... knock sensor fault, significant knock detected, sudden loss of oil pressure signal, faulty ECT, damaged wire harness and so on.

Fuel pressure is a possibility but I don't believe it is very likely... It won't hurt to check the pressure though.

Have you checked the mechanical timing and timing belt already?

I'll look back over this this weekend and see if/what I've missed and let you know if I can think of anything to check next. Worst case scenarios we start back at the top and work through the list.

No, Toyota does not make various thicknesses of exhaust gaskets. The gasket will compress somewhat after initial installation but nothing significant. The exhaust may just be hanging up on the studs in which case releasing the hangers may help.

How to make sure the hoses are tight enough.... hmm... No easy answer I'm afraid. If they're the right size you would just need to be sure the nipple is clean of buildup, corrosion and pitting and then use the proper constant tension clamp that Toyota put on at the factory. If you think the CT clamp has lost some of its elasticity then get another from Toyota. If you've switched to a worm gear hose clamp... well, just tighten until it stops. If it feels like it's too tight and is going to come apart, well, it probably is and there is something wrong with the nipple or the hose.

I know how you feel situations like this suck. You just need to make an actual list of how and what to check and in what order, set aside a few hours on Sat and Sun and hammer through it (TSRM in hand).