Hesitations caused by bad... Throttle or TPS

93, 3.0L

The engine hesitates on accel. Gear shifting sometimes taking longer than expected. I got new wires, sparkplugs, distributor cap, fuel filter. EGR is OK, transmission is OK, cooling is OK. No codes in the computer.
The transmisssion mechanics said that the delayed shifting could be caused by bad signals to the transmission. For example, the speed and throttle position don't agree.

In any case, the Haynes manual point to:
1) Vacuum leak caused by loose bolts/nuts on throttle to body connection. Do they mean the throttle to air plenum? Or do I have to remore the air plenum to access these? Do these normally get loose? (It's in the tune-up and maintenance section) Is there any other location with common air leaks?

2) TPS (throttle position sensor) This is a simple pot (resistance changes with rotation). The book does not list the normal resistance. Do these get dirty? If I remove it, can I blow air while turning it quickly to clean the internal wiper.

3) Is there a Distance/speed sensor? The book says that it's on the "transaxle extension housing" Where is that?

Thanks for the help

Speed sensor located at the small end of the tranny, fuyrthest from the engine. Iv'e taken mine out once and it was clogged with metal particles from the transmission.

The throttle position sensor is indeed a pot (potentiometer), but it is a sealed unit, not cleanable - except the leads on the outside - and therefore must be replaced if it is the culprit. It is probably worth replacing too since they're not too expensive ($25-$45), easy to access on the throttle body, and it will eventually fail anyway. When they fail it is generally due to the resistive material on the inside being worn down over time from the wiper abrasion. When this happens it can fail completely or just cause the engine to stutter when the wiper brushes over a certain area. Many times it will set off the Service engine light because during that time period the ECM goes into a default engine management mode because it is not receiving a TPS input.

The Hanes manual is referring the throttle body base gasket (where the throttle body bolts to the intake plenum). Basically any leak that will affect performance in that way would have to be physically downstream of the throttle plate. I doubt that a vacuum leak is your problem based on your description. Specifically, you didn't describe the idle really being high (1400+ rpm) which is a dead givaway for a vacuum leak on a fuel injected engine (disconnect one of the vacuum lines off the engine and see what happens). Incidentally you can track a vacuum leak by spaying carb cleaner on the lines until you find the spot where spraying causes the idle to drop momentarily. This is cause by the richening affect of the carb cleaner.

Speed sensor: The computer reads the same information you see in the speedometer through the speed sensor. Unless you’re getting erratic speed indications on the speedometer I doubt this is your problem.

Thanks for the info.

I did tight the throttle to plenum bolts. One bolt was really loose.
I also cleaned up the PCV valve. I was little dirty.
I removed the TPS and using a multimeter, it appears that there are no dead spots on it. (Since it's fairly inexpensive, I will eventually purchase a new unit) I have to say that the car was running a little better, so it could be a combined effect of a few things.

Idle RPM are normal. If I disconnect a vacuum hose, It does increase.

Speed sensor: I'm not getting erratic indications but I think that I'm getting slow response. If I press on the gas, the needle indicator increase, then it slows down for 2 seconds, then jumps up (by 5 MPH), then increase normally, then slows down again, jumps up.
I does not do this all the time. I don't have the RPM display and it's hard to tell if the van accelerates smoothly. I will pay close attention to this the next time it happens.
Is the sensor hard to remove? Do I need to purchase a gasket.

Thanks again

Seb