Locating (MAF) and Throttle Body

[Road_ster]

Hello, can anyone guide me where exactly I can locate the throttle body and Mass Airflow Sensor (MAF) on a 1998 GMC Safari Truck? Can it be accessed from under the hood, or from the inside?

[Blue Bowtie]

The MAF is accessible from under the hood. It is in the intake ductwork right behind the air filter box.

The TB is mounted to the top of the intake, and while it can be seen from the hood side, it is best accessed by removing the doghouse from the interior. If you only need to look, you can get at it from the hood side. If you need to clean it, clean the IAC, or otherwise inspect it for any reason, start removing the covers inside.

[Road_ster]

Thank You, the reason for my question was because I'm planning to clean the MAF and the throttle body. I'm experiencing a little bit of rough idleing when in Park especially when the engine is fully warmed up. I've already changed the rotor and cap, but I noticed that out of the 2 screw mounts on the distributor (that hold it down in place), one is chiped/cracked. I'm planning to change the distributor since it's old already. While I'll get that done, it would be best for me to clean the throttle body (since the inside engine cover is opened. Can you give me some advice on how to exactly remove the throttle body so I can get it cleaned? Do you think I should clean the IAC? If so, how? Will doing these things also solve the rough idle?

Thank you for your response.

[Blue Bowtie]

Rough idle is not likely caused by a throttle body or IAC problem. Wandering or inadequate idle RPM would be more likely the symptoms of those.

The MAF itself could be presenting an erroneous reading which might create an improper mixture, and carefully cleaning it with electromotive cleaner should be safe enough.

While the dog house is open, check all vacuum hoses, including the hard nylon ones in front of the TB and on the left side of the engine (where the intake vacuum tap is mounted). Those are prone to failure after years of heat/cool cycles and vibration. Also check the PCV valve.

Most likely the rough idle is related to an ignition or fuel delivery problem. If the spark plugs are in good condition and properly gapped, the plug wires are intact, and the distributor cap and rotor are intact, the problem could be the poppet injectors, FPR, or leaking line set in the intake.

Regarding the distributor cap, if there is a misfire with a new cap, make sure he cap is still intact. Many aftermarket caps suffer break down of their internal bussing insulation quickly, and the only method or testing is with a HIPOT tester or meggar. Delco caps are the only way to go for the W engine. You can find many instances of aftermarket cap failure in these forums. For most engines, it reaally doesn't matter, but for some reason the aftermarket just doesn't have these caps right yet.

If the ignition is intact, fuel delivery is correct, and there is still a misfire, a compression or cylinder leakage test might be in order to check or leaking valves or rings.

[Road_ster]

I want to do a full cleaning of the Mass Airflow sensor, but I'm not sure exactly where it is? I have a 3 wired connection going to a small rectangular box that sits on the right of the black air intake pipe, really close to the air filter housing. I also have a 2 wired connection that connects to something sitting in the black intake housing at the top of the pipe, more furthur away from the air filter housing. Which one is the mass airflow sensor?

I think it is the three cables connected to the rectangular box. This is how it looks like, except the box isn't at the top, it is on the right side. IF this is the MAF, can you tell me how to remove it?

What is that other 2 wired plug that sits inside the intake?

[Blue Bowtie]

That is a graphic of the MAF on your van. You only need to loosen the hose clamps at either end to remove the intake ducts from the MAF. The connector is on the right because of the length of the wire harness, The rotational orientation of the MAF is unimportant, but there is an inlet and outlet end.

The other sensor in the intake duct is the IAT (Intake Air Temperature) sensor.