Tech Area

Red Manifold (4 Cylinder)

Question: I have an 84 4 cylinder 4 speed. What's happening is that the exhaust manifold is turning red hot after just a couple minutes of running. It idles high (~2000 RPM). From what I can see is that it is getting too much fuel and not burning it all in the cylinders, sending the excess fuel into the exhaust and burning it there. Replaced or tested successfully.
a) temp sensor
b) EGR
c) IAC
d) all hoses
e) vacuum leaks (none)
f) O2 sensor
g) timing perfect
h) I even swapped the ECM with another identical car.. no change.

If I unplug the MAP sensor the car dies. Spark plugs indicate it's running rich. I am at a total loss. I have read everything on your web site several times over, but the closest I can find on your site is the same scenario, but running lean, not rich. I have not driven it since I did the work listed above. Will driving it really reset the ECM and fix itself? I have unplugged the battery many times to reset the codes.

Answer: Several thoughts about your problem.

Idle is above what IAC is capable of, so disregard that code. Running engine for long enough to reset the computer probably won't lower idle. It takes a lot of air for the idle to be that high....fuel alone will not do it. Computer will adjust fuel to match air intake.

So, would first check to make sure throttle plate is closed. Either plate shaft or throttle cable could cause it to allow air past the plate.

If plate is fully closed when engine is off or running, then there is air entering the engine beneath the plate.

Possible sources:
1. PCV valve/hose
2. Spacer/gasket between TBI and intake.
3. Intake gasket between manifold and head.

There are 3 temp sensors on the engine. If the one in the thermostat housing is bad, it could cause the ECM to think the engine is cold at all times. That could cause a high idle and "sooted" plugs, but doubt it WOULD?? cause that high an idle (beyond the ECM's control of the IAC). Same would be appropriate for a faulty TPS.

Therefore, it seems as though the engine is drawing in air from somewhere.

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