Any help on this one would be greatly appreciated!

I have an '88 S-10 with a 2.5L and 5 speed gearbox. Bought the truck used about 18 months ago, and all was fine. I used it as a daily driver until it suddenly started "bucking", which sounds like the truck is blowing back through the carbeurator. This only occurs when the truck has been warmed up, the truck is accelerating in the gears 3-5, and the accelerator is at about mid pedal. The bucking continues until I take my foot off the gas, or hold it almost completely to the floor. The timing is correct, a tune-up has been performed, the intake manifold has been replaced, the accelerator pump and injector have been replaced, and all of the vaccuum hoses I can find have been replaced.
One suggestion was the EGR valve. Do I clean it or replace it? Is there something else that may be suspect?

Thanks to all who can give me the answer.

Might as well clean it first. Its a whole lot cheaper than replacing it.

Your timing chain might have skiped a tooth.
Why would you replace the intake manifold unless it's cracked?

I had the timing checked and it was good. It also runs like a scalded dog when it wants too!

I meant to say that the intake manifold GASKET was replaced. This was done on the advice of Pep Boys. I paid $78.00 for them to tell me that, but they "don't do that type of work" so it was done in front of my house. Still didn't change anything.

$78.00 for that advise!Damn.

Just clean out the egr valve it usually has something to do w/ your problem. How are your plugs/wires? Check every inch of the wires and check the plug gap and for a fouled plug or two. These are the first (and cheapest) things you should do.

Tried cleaning out the EGR valve, but on the test drive, it started bucking again. I stopped, plugged the vaccuum line for the EGR valve, and tried driving again. The problem was just as bad as ever, so it isn't an EGR valve problem. Unless anyone can give me a great suggestion, it goes to the mechanic next week.

Thanks for the suggestions, anyway.

Any error codes ? U can check yourself. Lots of notes on here how to do.

check the check engine codes

Is the check engine light on?

How about a new fuel filter?

The "check engine" light has come on intermittently, but not necessarily in conjunction with what has been happening. I am sending the thing in to a somewhat reputable mechanic tomorrow to see what he can find.

I did change the fuel filter, but no luck. I'm thinking the fuel pump next, but I will give this guy a chance to prove me wrong.

You need to hall your but over to the local Autozone and have the codes checked.

If the light is coming on and you are not checking it, you are ignoring the real cause.

The check engine light is flashing for a reason, why haven't you had the codes extracted?

Get the codes checked and bring the EXACT numbers here so we can diagnose for you.

Thank you for the Autozone suggestion. I didn't know they did that.

Now for the findings. My 88 S-10 has an OBD1 computer system. The AutoZones around here only scan the ODB2 systems (96 and newer). However, they will sell me the scanner for $230! Think I'll wait on that one.

I will try unplugging/bypassing the O2 sensor tomorrow to see if that affects anything. If anyone has tried this trick already, did it work?

What is your engine vacuum reading. Sounds like its running lean

Ok, guess I am showing my ignorance here but, I didn't think a TBI had an accelerator pump. OR, if this is a carb, that there would be an injector.

Carb has pump TBI has injectors

distributor?

In my experience, if you cannot accellerate half to full throttle in mid and high range RPM's, it has something to do with the plug wires not being able to get enough current to the plugs. I had this problem with my car, I would accellerate and it would go waaaaaaaaaa- then I would give it even more throttle and it would go -bubububububub... until I let off of the throttle.

I checked each wire, took it off and looked at the connections and put them back on and the car ran perfect ever since. Didn't skip one slight bit. It was just a loose plug wire.

Do you have a carb or TBI.
They way to talk about it made me wonder???
TBI has injectors on the top of it 2 of them.

Fireplug, that was my point in my post. In the original post of this thread, he said that he replaced the "accelerator pump" and then said he replaced the "injector".

I am confused....Where's the original poster of this thread?

I guess we will have to wait and see if he returns with the info.

Sorry for earlier confusion. The truck has a TBI, and the part I replaced was the Fuel Pressure Regulator Diaphram. Looks like an accelerator pump....

I am having the codes read at a service station tomorrow, although the "check engine" light currently isn't on. I will try to get the vaccuum pressure checked again to see what that shows.

For giggles, I am disconnecting the O2 sensor this afternoon and taking it out for a run down the interstate. I am interested to see if that makes a difference or just makes it worse.

WOO HOO!! I unplugged the O2 sensor and took the truck for a l-o-n-g drive down the interstate and around the back roads. Not so much as a hiccup!

I will have to go get a new one later, but they are only $19 dollars. The most aggrivating part is that I suspected the O2 sensor when I went to Pep Boys in the beginning, but they insisted this wasn't the problem. Live and learn.

Thanks to everyone that helped out. See you when the next problem arises.

Did you ever get the codes scanned?

The computer would have picked up a bad O2 sensor.