Following up on my old thread, I ran the OBD 1 thing in socket 2 mode 1, got a code that reads 1-2-1 indicating a fault with the AMM, tried starting the car with the AMM unplugged and it would start perfectly fine in limp mode.

Prior to my ownership the car was run briefly with a failing water pump and a stuck mechanical thermostat, the owner always topped off the coolant when it began to overheat, but I understand that the AMM is very sensitive to excessive heat. I've replaced the pump, hosing, and removed the thermostat.

The headgaskets and other bits are fine, no coolant in the oil. Should I go ahead and replace the AMM?

The car doesn't stall out on the road, but occasionally hesitates, almost always stalls on start up with the AMM plugged in (or the idle surges), regular idle is a little unsteady and the fuel consumption could be better (running on premium).

 

the AMM is senstive to excess heat in the intake air. on the 240's, there's a heat riser collector thing on the exhaust manifold, thats connected to the bottom of the air filter box via a piece of what looks like clothes dryer vent hose... in the bottom of the air filter box, there's a thermostat controlled air flap. these fail open, causing the engine to get hot hair off the outside of the manifold. I always wire those flaps shut with a bit of bailing wire.

note that thermostat on the air flap is NOT the main engine coolant thermostat on the outlet side of the water pump.

 

I've pulled the air flap out, the metal hose is still connected but the engine temperature usually stays below mid way, the "compensator board" has been yanked and temperature gauge re-wired.

I've heard that unplugging the AMM while the cars running isn't the best idea, I did it just once not knowing this. The car was having trouble starting beforehand though.

 

wait, you removed the air flap?? you want it SEALED shut for most conditions. its only supposed to open when its well below freezing, as engines don't like air thats /too/ cold.

 

Yea, accidentally bent the brackets that hold it in, I should be sealing up the hole for the heater hose later on today.

 

Just removed the pre-heat pipe, I still have the air flap and could probably re install it with a little tape or something. With Spring coming up I'm going to just cap off the pipes air box port for now.

The 25A blade fuse under the hood looks okay but the holders quite filthy, I'll probably replace it with a holder that has a cap.

 

note that heat riser hose is a inspection item as part of a smog test, at least in California, and likely other jurisdictions... noone checks the flap, however.

 

Thank you for that note, where I get my car inspected they don't check for that metal hose on an older car, just lights and windows..