proud 1st time owner of 87 supra turbo
 

This is my first supra and I want to learn all I can about the car from regular maint to performance upgrades. But my first question I have is is there a way to determine if my head gasket has been changed recently? I changed thehead gasket on my 95 accord myself and I realized there is a small ledge coming off the block that the corner of the gasket sits on that was visible after the motor was put back together. It was very obvious the. Gasket was changed. And I'm just curious if there's A way to tell on these supras

And also when I really get on it then let off the gas really quick my car dies. I read on another forum that it may be the blowoff valve. Could that be the case?

I don't have an answer for your hg question, but running a blow off valve (vented to atmosphere, not recirculated) can cause your engine to stumble and/or die when shifting. This happens because all of that air passed through the AFM, so the ecu expects the air that was just dumped to still be in the intake. The ecu then provides the amount of fuel to the engine needed for the volume of air it thinks is still there, causing it to run excessively rich.

You can eliminate this problem by running a bypass valve instead of a blow off valve (easy) or by running a system like MATT-PRO 2 (?) in speed-density mode (not exactly sure if that's correct; in any case this would be a better setup because you can eliminate the AFM, but my understanding is that it's incredibly difficult to set up). A search on the forum or Google should bring up several results for this particular problem, as it's very common

This may be a dumb question but what is the difference between a blow off valve and a bypass valve? My car is completly stock except the catback exhaust I might add. So if either one of those is aftermarket my car does not have one. I just assumed that since my car was turboed it had a blowoff valve. Just not one that made sound when it releases pressure

Typically, a bypass valve vents excess boost back into the intake after the AFM, whereas a blow off valve vents the excess boost out of the intake into the atmosphere. If your car is bone stock, it should have a bypass valve and shouldn't be suffering from the issues people with blow off valves have. I'd start diagnosing by checking for engine trouble codes and inspecting your intake and vacuum lines for leaks.

I checked my trouble codes and I believe. 24 41 51 came up. Ill start checking my vacuum lines. It doesn't do it when I rev the motor only driving when the turbo kicks in

There may be vacuum line problems but the code 41 and code 51 are going screw with throttle state transitions (ie: the ECU cant's tell that you're flooring it until it's been floored for a few seconds already and it has a difficult time knowing when it's supposed to start modulating the ISCV for proper idle). The code 24 is going to screw with your fuel mixtures. While code 51 could just be an alignment issue the code 41 indicates damage in the TPS or its wiring.

I don't entirely understand your question about the head gasket. Yes, there is a ledge which protrudes out from under the head on the driver's side. It's supposed to be there. What else are you asking?

Well I know my alignment is off and I believe the 24 code came up because I disconnected the o2 sensor for a minute. I hooked it back up but it still read.but I guess my main question is why would my car die after I floor it then let off the gas?

Code 24 has nothing to do with the O2 sensor.... N O T H I N G.

As I've mentioned, all of these codes are in one way or another capable of affecting your throttle and idle transitions. Please don't make me bang my head on my desk.... I do that far too often around here. You've proven you can check for codes. Now go that extra three feet and fix them. There are many things which cause the stalling... I suggest we speculate on the other possibilities AFTER you fix what your ECU is already telling you is suspect.

Welll I think I solved the stalling issue. There is a little adjustmentbolt/screw where the actual throttle rod meets the rest of the throttle body. I adjusted that and the stalling stopped. I figured it was snapping the throttle all the way shut before. I still have code 24 tho. So if its not the o2 sensor what is it? I only thought that cuz I read it on another forum.

When he throttle is closed... guess what... it's supposed to be CLOSED. Quit dicking with things you have no idea about just because you think it might be a good idea and go buy a service manual. The idle is controlled via a computed controlled valve which bypasses the throttle body altogether. Your code 51 indicates a possible problem with the switch that's built into the TPS to tell the ECU when the throttle is closed.

Look in the MKIII FAQ section for a thread on diagnostic codes for a list and descriptions of the various codes.

Look I'm here to learn. I'm pretty good with cars but a supra is a lil more complex the a 95 accord so gimme a break here. Now I do realize that code 24 is an air fuel mix issue. So. Could my afm be the culprit? U answered my question on another thread about using a different afm by the way which I appriciate. And I do plan to get a service manual but moneys short right now. The car as I said before is my daily driver. It runs good just little things id like to take care of before I start getting really indepth with it. I appriciate the help and sorry for making u bang ur head on the desk. Like I said I'm new to the supra scene. Oh and I checked my codes again and 41 was not the right code it was 31. So 24 31 and 51 are the codes that it throws fyi. I'm. Mainly focusing on the air fuel mix right now tho.

Yes, and I'm here because I find some weird sort of joy in continuing to work after I've already clocked out. ;) I'm always more than happy to help (my wife reminds me about it all the time... especially now that I'm rebuilding my 80 year old neighbor's 1946 Harley for free) but I'm not going to completely spoon feed anyone.

The diagnostic information you need is already present, I've told you where to look for it and I'm not convinced you've even looked at the FAQ on what each code means. Had you done so you might have found that the code 51 is the easiest code to fix and only has to do with idle issues. Codes 31 and 24 are related to two entirely separate circuits in the AFM... so it is more likely than not the AFM's connector is damaged, corroded or unplugged. Sure, it's possible the two circuits have both failed or the ground line the both share has been damaged but it's not the most common issue. Look in the service manual (again linked to in the FAQ section) for information on how to test the AFM and how to calibrate the TPS.

This is not a hard car to work on at all. Newer cars (incl. '95 Hondas) can be MUCH worse. They're just not as old, beaten up by teenage owners, have cheaper parts and a much better on board diagnostic system.


BTW - This is one of the easier going Supra forums and I'm not being a hard ass at the moment.



EDIT:

Aw hell, here you go:

Diagnostic codes and what they mean.
TSRM - Toyota Service and Repair Manual - It's for a '91 but the majority of information is consistent with earlier models.
TPS - Throttle Position Sensor diagnostic and repair information. Code 51 ONLY related to the IDL switch circuit and calibration.
KVAFM - Karman Vortex Air Flow Meter diagnostic and repair information.


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Hey I appriciate that. And ill check out the faq I'm still figuruing out how to navigate this forum plus its from my phone. But thanks for the help ill let u know what I discover.