Idle issue - drops rpm but recovers

Mybestsupra2 · 06-13-2016, 04:20 PM

Hi, it may be that the afm is bad, but before I would spend a lot of money trying to find a replacement, I would
1, make very sure that all the clamps on the air hoses and turbo hoses,(if a turbo), are tight. Makes a big difference.
2, Check and adjust if necessary the TPS using the TSRM as a guide. The 87 Service Manual is not correct in the TPS adjusting diagram.
3, Remove and clean the IAC, being careful to not lose the grommet and filter if it is a turbo.
The AFM's don't go bad that often, mostly what happens is guys try to clean them, and ruin them.
The AFM on the 7mge,(non turbo), can be gently cleaned with the proper solution, gently and not touching the wires with anything but a gentle spray and gentle air to dry.
The AFM on the 7mgte Turbo will most likely be ruined by attempts at cleaning. Many have tried and failed to clean this one. Best not to try.
I believe cleaning the iac, and adjusting the tps and tightening all hoses will fix your problem.
Luck to all.

Bru · 07-09-2016, 03:16 AM

Another thing to take a peek at is the function of the EGR valve if you still have one.
Run a vacuum line separately down to the vacuum actuator on the valve and put a mouth vacuum on it until it retracts completely to check that there are no air leaks in the diaphragm. Quickly release the vacuum to allow the spring to bust any carbon that might have accumulated on the valve seat inside. Do that a couple times with the engine not running. The manual test for the EGR valve function is to start the engine and then apply a vacuum to the diaphragm at idle. The engine should stall. To test the vacuum modulator follow the test procedure in the book but a real quick check is to apply mouth pressure to the connection on the bottom. If there's a leak in the diaphragm inside the modulator, air will pass through. Otherwise, it should hold pressure if it's working properly. I had a problem with a hole in this diaphragm which caused the engine to run funny at speed with no load on. It felt like the engine was pulling and pushing. When I replaced the defective vacuum modulator, the problem went away.

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06-13-2016, 04:20 PM	#1
Mybestsupra2 Stock Join Date: Feb 2016 Location: Pa Posts: 2	Hi, it may be that the afm is bad, but before I would spend a lot of money trying to find a replacement, I would 1, make very sure that all the clamps on the air hoses and turbo hoses,(if a turbo), are tight. Makes a big difference. 2, Check and adjust if necessary the TPS using the TSRM as a guide. The 87 Service Manual is not correct in the TPS adjusting diagram. 3, Remove and clean the IAC, being careful to not lose the grommet and filter if it is a turbo. The AFM's don't go bad that often, mostly what happens is guys try to clean them, and ruin them. The AFM on the 7mge,(non turbo), can be gently cleaned with the proper solution, gently and not touching the wires with anything but a gentle spray and gentle air to dry. The AFM on the 7mgte Turbo will most likely be ruined by attempts at cleaning. Many have tried and failed to clean this one. Best not to try. I believe cleaning the iac, and adjusting the tps and tightening all hoses will fix your problem. Luck to all.

07-09-2016, 03:16 AM	#2
Bru Bone Stock w Upgrades ;-) Join Date: Apr 2010 Location: Tampa Bay Posts: 213	Another thing to take a peek at is the function of the EGR valve if you still have one. Run a vacuum line separately down to the vacuum actuator on the valve and put a mouth vacuum on it until it retracts completely to check that there are no air leaks in the diaphragm. Quickly release the vacuum to allow the spring to bust any carbon that might have accumulated on the valve seat inside. Do that a couple times with the engine not running. The manual test for the EGR valve function is to start the engine and then apply a vacuum to the diaphragm at idle. The engine should stall. To test the vacuum modulator follow the test procedure in the book but a real quick check is to apply mouth pressure to the connection on the bottom. If there's a leak in the diaphragm inside the modulator, air will pass through. Otherwise, it should hold pressure if it's working properly. I had a problem with a hole in this diaphragm which caused the engine to run funny at speed with no load on. It felt like the engine was pulling and pushing. When I replaced the defective vacuum modulator, the problem went away.