1990 K1500 Throttle Issues

[ericmb55]

I have a 1990 K1500 with a 350. I have noticed that there is an issue with the throttle response. When the gas pedal is pressed, the engine stumbles before picking up. Also, after the engine has been reved, it takes a bit longer for it to idle back down than most others. What could be the problem? The fuel consumption has gotten a little worse than normal. I have lost about 2mpg. I have replaced IAC and put a kit in the fuel meter assembly and replaced the regulator diaphragm. I really hate to start with the sensors without any idea of what might be wrong.

[2000CAYukon]

I have the same truck (only GMC). Unfortunately, this can be many things. First thing is to verify fuel pressure - 9 to 13 PSI. You do need a special tool to check fuel pressure on TBI trucks (no service port). When was the last time fuel filter was replaced. Also a good idea to do a complete Tune-up (if you have not already done that).

If the fuel pressure is good, I would recommend getting it scanned to see if you are running lean or rich.

Fuel deliver is controlled by O2 sensor, ECT sensor, TPS and MAP sensor. A leaking MAP vacuum hose, or bad MAP can cause excessive fuel consumption. Any of these sensors could cause your issue. Scanning to see what the sensor are reading is better than throwing parts at it.

Other possiblities could be partially clogged exhaust, worn timing chain or improper EGR valve operation.

//2000CAYukon

[ericmb55]

I have read the threads that have suggested that the TPS or the CTS could be the problem. I haven't really thought about the timing chain or gears. The truck has 130K on it. I have changed the tires back to 265/75/16. I had put 285/75/16 on it and it just became sick. No power at all and I was getting 9 mpg at times. I checked last night and it got 15mpg. This is much better but it is still not running right. It seems to go through the normal high idle while warming up but it surges during idle after warm up. It's almost like it can't decide how much fuel it needs. I have also noticed that it will surge while driving if it is put under a load such as going up a hill. I'm thinking TPS but I don't know how to set it right if I change it. Any thoughts?

[2000CAYukon]

A surge can also be a vacuum leak. In my case, I found that the PCV gromet was no longer sealing as well as the vacuum hose to the MAP sensor was leaking. These fixed, really helped my rough idle that I was fighting at the time.

With a 130K on the clock, is the O2 sensor original? How about the EGR valve?

In order to replace the TPS, you need to remove the TBI and drill out 2 rivots. Minor adjustments can be made using a meter or scan tool and move the TPS.

I doubt this issue is your TPS (but could be wrong). I suspect, this is more to do with wrong fuel delivery. Either a weak fuel pump or bad O2, MAP sensor or vacuum leak. EGR or exhaust issue is also a possibility.

Good Luck,
//2000CAYukon