1994 Chevy Blazer Jerking when driving.

When the jerking condition exists do the engine rpms jump for an instant or does it seem like you've just hit the brake once? It could be the convertor or the convertor lockup solenoid in the transmission. Another thought is the trans may be dropping out of OD into drive and back up in an instant. Please advise.

Your tach gets it's signal from the ECM. If the ECM thinks the engine rpm has dropped, it may be telling the trans to downshift even for just an instant. It may be such a thing that it is going into drive before it's left OD. Just a theory. If you have access to a mobile diagnostic unit like an OMB 2 or similar, you can monitor rpms and shifting patterns going down the road. Let me know your thoughts on this. I really don't it's a torque convertor problem unless I'm missing something here.

OK, now it's making sense. If I'm correct this condition is happening when you are in drive also, BUT, when you're in OD, the engine rpms and power curve are lower so the hesitation is more pronounced. I'm thinking now that you have a "dead spot" in your throttle position sensor (TPS). Apparently, you are not getting a check engine light. Cruising down the road the throttle is usually held pretty much the same position. After a while this will wear a dead spot in the TPS. Once in a while when hitting this spot, the signal to the ECM drops out for just an instant and shuts down the fuel injection. All the ECM knows is that you took your foot off the gas, even though you didn't. We can test this theory with an ohm meter at the TPS. Testing accross TPS terminals A & B for a V8 or B & C for a 2.5. The meter reading should rise and fall smoothly from idle to full throttle. If it falters at all, there would be your problem, or you could just change the sensor. They're not that expensive. Also, this condition could be happening so fast that the ECM can't pick it up to register a trouble code. Let me know what you find.

You should be able to change the TPS yourself with basic tools. The TPS is mounted on the passenger side of the throttle body unit. It's on the opposite end of the pivot shaft that the throttle cable mounts to. Usually held on by two TORX head screws. It may or may not be adjustable, but if it's adjustable, you can usually set the idle speed by ear. If you have, or have access to, a fax #, I can ship you a location sheet. I can attach it to this sight, but they don't come through very well.

Willy, fax is on it's way.
On your water pump. Located on the bottom of the pump is what's called a "weep hole". You usually need a mirror to see it. This hole allows coolant to escape from the pump before it gets to the pump bearing in the event the pump seal starts to leak. If the pump seal is indeed leaking, water coming out the weep hole, it means the pump is on it's last leg and should be changed. The "wiggle", could be the pump bearing, the fan clutch bushing, or a combination of both. To answer your question, neither should wiggle.
What is supposed to be wrong with the intake gasket? Is it supposed to be leaking coolant or air? GM V6's are noted for leaking, but not V8's.

Good, keep me posted.

I have so many post active right now, I have to re-read them to make sure what I'm dealing with. In going over your's, I had a thought on the intake manifold leak. The ECM will compensate for a vacuum leak by richening the fuel mixture trying to maintain the 14.1 to 1 ratio. BUT, the ECM's ability to richen is only up to a certain point. If cruising down the road and the ECM has richened to it's maximun ability, and you accelerate just slightly (open the throttle plate), the mixture will lean out too much and it will "lean cough" or "buck". You mentioned you had some broken bolts on the intake. Are these the bolts that hold the manifold to the head? If I'm correct, this would explain the problem. You can test for intake leaks as follows. Some people use a spray bottle of water for the test. I've always prefered a spray can of ordinary carb cleaner, but you have to be careful, we don't want a fire. With the engine at a warm idle, liberally spray down the area where the intake manifold meets the cylinder heads and around the throttle body. If you hit an intake leak the engine rpms will jump up for a few seconds, then return to normal. I wish I had thought of this earlier, but I didn't pay enough attention to the intake issue. Let me know what you find.

Firefighter, huh? Not to patrinize you, but you guys are my hero's. I was in a volunteer dept. Many years ago. It's a lot of training.
Exhaust manifold, you say. Well that blows that theory. Yes, an O2 sensor can make an engine run rich or lean which can screw up the fuel mixture. They can do this and still stay enough in range where they won't set a trouble code. It's rare, but it does happen. I'm beginning to feel like an "ene', mene', mine', mo', parts replacer here. I wish I could run the truck down the road just once. If you had access to a mobile diagnostic unit, we could plug it in and take a short road trip. This will allow you monitor the sensor perameters under realtime conditions. An O2 sensor is like a battery. It puts out.1 volts at cold idle(rich) to.9 volts hot (lean). Is this kind of a test possible? Note: The O2 sensor can also be tested when removed and heated with a propane torch on a volt meter.

It's a good thing you brought Autozone up. They will do computer diagnostic checks for free. They may even let you barrow their unit. This would sure help narrow this problem down. Quessing makes things difficult not to mention expensive for you. Let me know.

Looking for any stored trouble codes and the voltage output of the O2 sensor(s).