Hesitation..Kinda Sorta...
 

I have a 2001 Blazer 4.3 Auto that has developed a strange 'hesitation' of sorts. It doesn't misfire, surge, buck, or feel like transmission slippage...it feels as though the brake is being applied then released. It doesn't matter if the vehicle is cold or up to temp, or whether I'm on a flat surface or a hill. It only happens when up to speed (cruising) but the rate of speed doesn't matter. It happens at 35mph on an arterial or at 60mph on the freeway. Sometimes it will happen 2 or 3 times in a day, and other times I can go for a week or so without it happening. I had it scanned and was told there are no codes in the computer. No drop in rpm...fuel pressure checked okay under both load and no load conditions. I've done a couple of searches for info on the forum but didn't see anything related to what I describe. Any idea what might be causing this to happen?

Just a thought, but is your A/C on at the time? (Your air conditioning compressor also runs when in the defrost mode). I experience the same thing your describe when my compressor kicks on and off and have seen other posts on this forum describing similar.

Mine does this as well, but only at slow speeds. It is with the A/C running and usually when I'm pulling off from a stop. Truck will feel like a stutter or a sudden loss of power. I'm guessing its the compressor motor... only reason I say that is my friend here has a ZR2 pickup of the same year as my Blazer that suffered the same issue. He had a coolant leak and had to replace his compressor... now it runs like a champ.

Its a thought, but this could be caused by many things. When was the last time plugs/wires/rotor etc were replaced?

Thanks for the replies. The A/C is off, blower motor in position 1 and vented air. The truck accelerates with no problems both from a standstill or acclerating to pass. It's once I'm up to cruising speed that this happens. It literally feels like the brake is being applied then released. Sometimes it's for just a brief second and other times it may last for 5 or 10 seconds. I just purchased the truck recently, and it didn't do it the first couple of weeks. No idea the last time it had a tune up, but it will be getting a new rotor, cap, wires, plugs, pcv valve, air & fuel filters this weekend.

When you do your tuneup process, clean the EGR valve as well. There's a great thread in the DIY section here that tells you what to do. I did it, and my gas mileage went up a few MPG.

There were no codes when the computer was scanned, but I'll pick up an egr gasket and clean it - thanks for the reply.

Not just the gasket... there's a whole metod to cleaning out the EGR Valve. Check this out:

https://blazerforum.com/forum/showth...ight=EGR+Valve

What's the best way to get to the EGR valve on a 95? It looks like it's buried under there. Do I have to remove the throttle body, or will just the serpentine belt tensioner (and possibly the A/C compressor) be enough?

After reading your 1st reply about the egr valve I did a search and found that thread. I plan on cleaning the valve - carb cleaner, bristle brush, etc - prior to reinstalling it. :icon_wink: Thanks again for the reply.

Well, I've been driving the '01 Blazer for a couple of days now after giving it a tune up (rotor/cap/wires/plugs/air & fuel filter), cleaning the egr valve & map sensor but the random 'hesitation' is still there. Anyone have an idea as to what may be causing it? There are no codes stored in the computer. It idles and accelerates fine, but once you're up to cruising speed every once in awhile it feels like the brake is being applied then released. It sure has me baffled.