Had a driveability issue that would cause the car to misfire at light loads. For example, revving to 1800-200 rpm would result in a bad misfire. Cruising at light throttle would result in a jerky feel although it was hard to actually hear the misfire, and throttle response off idle was poor.
On the 7M, often these types of drivability issues are due to a small vac leak, and I searched high and low for one. My accordion tube did have a small tear but replacing it did not fix the problem. I also checked the ignition carefully, but since the car had no misfire under boost I didn't really think it was ignition related.
My attention eventually focused on the EGR system. It sits there forgotten at the back and I had never looked at it in 25 years. I had read here of someone that had the rubber pipe between the EGR vac modulator and EGR valve fail, and so I wanted to check that out as well as anything else on the EGR system that could be tested. The location of the EGR makes it very hard to work on, and so its easy to forget about it.
Using some very large needle nose pliers I was able to disconnect the spring clamps and remove the EGR vac modulator from the EGR valve. The pipe itself was in good condition, it appears to be made of silicone with a cloth like heat should around it, but when I tested the vac modulator it failed every test.
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=EC&P=18
Apparently the diaphragm inside it had ruptured and exhaust was able to blow right through the tube and out the vac modulator air intake. Everything was black and grimy. The Q port also failed the test as it was permanently blocked.
The EGR valve diaphragm itself can be easily tested by hooking up a vac line and pulling vacuum on it. You should feel and hear the valve opening under very little vacuum (you can do it easily using your mouth) and it should not leak or hiss. There is a better test to verify it actually works described here:
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=EC&P=17
Now the bad news, the EGR valve, vac modulator, and the mesh covered hose are all discontinued. Also, the vac modulator is a 3 port design and most Toyota's use a 4 port design (even the 7MGE uses a 4 port identified by P Q R ports on the cap) . The only three port I could find was for the 2JZ-GTE. I have one on order and will test it when it arrives. Given it is for a 3L L6 it may work on the 7MGTE. There is an aftermarket vac mod (STANDARD MOTOR PRODUCTS Part # VS96) listed on Rockauto as a "EGR Vacuum Solenoid". It is more expensive than the genuine Toyota part and it may not be available if you try to order it. When I tried to order it the part disappeared off the catalog, but I see it is there now.
I ended up buying a used one. It passed the functional tests and after installing it all my drivability problems have gone.
Its definitely worth checking from time to time. You can do a quick test just by removing the P and Q vac pipes and running the vac tests. Only takes a few seconds. I suspect mine ruptured because the car has been running higher than stock boost for years now.
On the 7M, often these types of drivability issues are due to a small vac leak, and I searched high and low for one. My accordion tube did have a small tear but replacing it did not fix the problem. I also checked the ignition carefully, but since the car had no misfire under boost I didn't really think it was ignition related.
My attention eventually focused on the EGR system. It sits there forgotten at the back and I had never looked at it in 25 years. I had read here of someone that had the rubber pipe between the EGR vac modulator and EGR valve fail, and so I wanted to check that out as well as anything else on the EGR system that could be tested. The location of the EGR makes it very hard to work on, and so its easy to forget about it.
Using some very large needle nose pliers I was able to disconnect the spring clamps and remove the EGR vac modulator from the EGR valve. The pipe itself was in good condition, it appears to be made of silicone with a cloth like heat should around it, but when I tested the vac modulator it failed every test.
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=EC&P=18
Apparently the diaphragm inside it had ruptured and exhaust was able to blow right through the tube and out the vac modulator air intake. Everything was black and grimy. The Q port also failed the test as it was permanently blocked.
The EGR valve diaphragm itself can be easily tested by hooking up a vac line and pulling vacuum on it. You should feel and hear the valve opening under very little vacuum (you can do it easily using your mouth) and it should not leak or hiss. There is a better test to verify it actually works described here:
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=EC&P=17
Now the bad news, the EGR valve, vac modulator, and the mesh covered hose are all discontinued. Also, the vac modulator is a 3 port design and most Toyota's use a 4 port design (even the 7MGE uses a 4 port identified by P Q R ports on the cap) . The only three port I could find was for the 2JZ-GTE. I have one on order and will test it when it arrives. Given it is for a 3L L6 it may work on the 7MGTE. There is an aftermarket vac mod (STANDARD MOTOR PRODUCTS Part # VS96) listed on Rockauto as a "EGR Vacuum Solenoid". It is more expensive than the genuine Toyota part and it may not be available if you try to order it. When I tried to order it the part disappeared off the catalog, but I see it is there now.
I ended up buying a used one. It passed the functional tests and after installing it all my drivability problems have gone.
Its definitely worth checking from time to time. You can do a quick test just by removing the P and Q vac pipes and running the vac tests. Only takes a few seconds. I suspect mine ruptured because the car has been running higher than stock boost for years now.
