1985 p/u 22re manual/4x4

starts right up real quick usually, idle seems normal. all cyl's are firing
Can rev rpm's up from idle (around1k) to just about 2k without problem.
Any further throttle opening results in a pulsing/surging up and down b/t around 1k and 2k at about a 1 second interval,
regardless of throttle position (once up to and then beyond approx 2k).

Have new TPS installed, had no effect at all.

Any suggestions for diagnosing this?
Thanks!

 

just took a test drive and discovered something pretty weird (to me).

It seems to be driving normally, and if the truck is moving at all at any speed, either forward or backward, in gear or coasting in neutral, I can rev it up to and hold any rpm.
As soon as truck comes to a stop, it goes back to the surging and I can't get it to rev up without something cutting the rpm's.

 

Is there any connection to idle issues with the brakes applied? That may point to a bad diaphragm in the brake booster.

 

"Idle rpm cut" this is triggered by the ecu when it sees higher rpms and idle switch is closed. Something is wrong with the throttle sensor or its wiring. Make sure the tps is the correct one, installed and adjusted correctly and there aren't any exposed wires or shorts in the harness.

 

well, I've been driving it for a while now and it has been running fine, but it still cuts rpm's when given gas when truck is sitting still.
Temporarily assuming I've installed the correct TPS correctly, is it possible this could be an issue with the ECU rather than the TPS?
I don't recall what the I/O circuits are on the TPS, but I seem to remember seeing that of the two, the ECM is the only one that has a speed sensor input...
How would truck moving vs sitting still change the way the TPS is functioning or malfunctioning?

 

Not necessarily when it's moving. When the brakes are applied, moving or not.
There's a circuit in the ECU that cuts off the injectors when the RPM is above about 1K, when the brakes are applied. Toyota figured that when you're slowing down (brakes are applied) you don't need the engine revved up. So, if the RPMs are up, and you are pushing the brakes, moving or not, you'll get that surging. The ECU cuts the injectors until the RPM drops below about 1K, then allows the injectors to function again, thus the RPMs climb back up, the ECU cuts them again, rinse repeat.

If the idle switch in the TPS is shorted, ie permanently closed, the ECU will think the truck is slowing down when the brakes are touched, whether intentional or no, or you're stopped and holding the brakes, but are trying to rev up the engine, the ECU will cut the injectors because the ECU thinks you're at idle, and away you go. Or don't go, you know what I mean.

There is also, as mentioned above, a problem with the brake booster. The big round diaphragm behind the brake master cylinder, bolted to the firewall. If the diaphragm inside is failed, IE leaking vacuum, it can cause the surging as well. Easy enough to check. Pull it's big vacuum line off the throttle body, and apply vacuum to it. See if it holds the vacuum. If not, you've found the trouble.

Good luck!
Pat☺