The throttle position switch (square thingy opposite the
throttle cam) can induce surging if it was moved from the
factory set point. This helped me:
"Here it is. The prongs on the switch are labeled top to bottom, I, P and F. With the throttle closed, you should have no continuity between P-F and continuity between I-P. Slightly depressed gives no continuity between both of those sets of prongs and with it fully depressed (WOT), you should have continuity between P-F, but not I-P.
To adjust the switch, hook up the Ohm meter to I-P and place a 0.012 feeler gauge between the throttle stop and the throttle lever. Adjust the gauge until the point where the continuity is just established. Then use a 0.020 feeler gauge to make sure continuity is broken. At that point, it is adjusted.
Good Luck,
Michael "
Make sure the vacuum connections under the intake manifold haven't slipped off and that they are connected to the right points. That big tube for the air regulator can get a hole worn into it were it passes down through the intake manifold Check the underside of the tube that goes from the air filter to the throttle body too.
Cold start problems could point to the air regulator or the
ECM temperature sensor (threaded into the underside of the intake manifold toward the front of the engine; not to be confused with the temperature gauge for your dashboard). They work together on a cold start to increase the idle, kind of like a reverse choke. The temp sensor in the intake manifold tells the ECM to adjust the fuel flow of the injectors to run rich on a cold start. To keep it smooth the air regulator (under the intake, mounted to the engine wall)bypasses the throttle plate and runs extra air into the throttle chamber. If either of these is not right the cylinders will be either flooded or starved for air,
To Check Sensor: : There are two connectors on a bracket just behind the battery. The larger of these two has the 2 wires from the temp sensor in it. They are BLACK and GREEN w)YELLOW stripe on my 88 truck. The way the connectors are mounted these two wires are right on the top of the connector. Simply unplug the connector and put your ohmmeter across those two pins. Reading should be:
degrees F / K ohms
14 / 7-12
50 / 3-5
68 / 2-3
122 / 0.7-1
176 / 0.2-0.4
To check air regulator: Pull large tube off firewall side of throttle body. Cork both openings and start up. Pull the cork on the tube and quickly pull put your thumb over the tube. You should feel a strong vacuum. If you don't the regulator is stuck closed. If you do feel vacuum, it should diminish after a couple of minutes. If it doesn't diminish it's stuck open or no power is getting to the plug.
Make sure your grounds are good esp. to the intake manifold.
No ground=No signal.
I know that with hustling to get an engine back together, occasional shortcuts come back to bite the weekend mechanic (like me)so I've come to appreciate a little more time spent assembling avoids aggravation later. If you have fouled plugs on a recent rebuild that's not right. Do a compression check. If the bolt holes on the block had muck in the bottom of them it could be that the torque values you had when bolting down the head weren't accurate and the head gasket is passing a bit. Could also be a bad injector or the valve adjustment is off. It doesn't take many miles to burn a loose or tight valve so make sure they are adjusted cold.
I cooked my head by not filling with coolant properly. The head and the intake manifold have galleries that can trap air if it's not vented. One way is to park on a slope engine on the upside, pull the radiator cap (cold engine; don't want a face full of hot coolant) and let the engine reach operating temp. When the thermostat opens it should burp the air out the radiator so just top up with coolant.
I prefer the direct approach, unscrewing the air by-pass valve out of the top of the thermostat housing (again cold engine)and filling the radiator until coolant comes out the
hole. Or do both! I'm just tellin' ya, parts of the aluminum head will melt if there's air trapped in it and the temp sensor in the intake manifold will give a false reading if it's not submerged in coolant... plus your water pump can't pump through air... it's all bad. Make sure it's full. Hope this helps. Makes me miss my p'up.
