89 Chevy s-10

I'm a little lost as to what to try next and hoping some of you may have an answer. The truck causes bucking going down the road and will stop when you push on the gas. Also it does it less in colder weather. The truck has had modulator sensor put in 2'x. One time the o2 sensor but that was 4 years ago. The PVP valve you can blow out one end and have blown the line out. The modulator sensor will work lose at times and then its constant bucking. You pull over tighten it back and then it is just happens every so often. Head gasket had to be put in over a year ago. The truck gets great gas milage and when it doesn't buck, it runs smooth, runs smooth at an idle. Help, this is really becoming a pain.

Is this an engine problem, or a transmission problem?

I had a similar problem with a barretta, it ran smooth when at idle, great acceleration, everything seemed normal except when cruising at aroun 55 mph it would start bucking, turns out a couple of spark plug wires were a little lose and at higher speeds vibrated causing the wires to lose connection causing inconsistant engine performance.

What is a Modulator Sensor?? Where is it located?
Never heard of that one before.
-Jim.

i dont understand your sentences!!!!!!!!!! what the hell is a modulator vavle? where is it? what does it connect to? do u have pictures? we can probable help you better with a picture of the part you are talking about.

i dont understand your sentences!!!!!!!!!! what the hell is a modulator vavle? where is it? what does it connect to? do u have pictures? we can probable help you better with a picture of the part you are talking about.

My thoughts exactly, what the hell is this person talking about?

I hate it when they make up names for parts.

I imagine that you checked the thing-of-ma-jig. Oh! I mean timing

My ex-girlfriends truck did that and it was just the timing being out a little. It was worst on hotter days too.

I have an S-10 .... similiar (almost identical problem), turned out to be the fuel pump.

I'm a little lost as to what to try next and hoping some of you may have an answer. The truck causes bucking going down the road and will stop when you push on the gas. Also it does it less in colder weather. The truck has had modulator sensor put in 2'x. One time the o2 sensor but that was 4 years ago. The PVP valve you can blow out one end and have blown the line out. The modulator sensor will work lose at times and then its constant bucking. You pull over tighten it back and then it is just happens every so often. Head gasket had to be put in over a year ago. The truck gets great gas milage and when it doesn't buck, it runs smooth, runs smooth at an idle. Help, this is really becoming a pain.

I am assuming that you are talking about the modulator diaphragm on the transmission. If it is working loose: A - it is not being installed to the right torque specs or B - The first time it was removed, the mechanic screwed up the threads. Your remedy is to have a reputable mechanic see what could be causing this. I can't help you and I highly doubt that anyone here can without actually looking at it.

On a another limb here but when you say PVP, I will assume you mean PCV valve. Change it, it is cheap.

and pcv valve is a DEALER buy not an advanced auto or autozone thing

I'm sure by now you've got the problem fixed. I don't understand... My 89 Astro should have the same transmission. It doesn't have a modulator valve, the ECM controls the lock-up torque converter (TCC). In my case it turned out to be a faulty throttle position sensor (TPS). It's basically a variable resistor mount on the passenger side of the throttle body. It's cheap and easy to replace, too. When the ECM got no signal from the open spot on the TPS it would unlock and lock the TCC rapidly. It shook the whole van!