97 Blazer engine revs every 5-10 seconds??

I have a 97 blazer, 4WD (4.3L), about 110K miles, and am having an odd problem. First, the engine has been idling very high (around 15mph) and it seems like whenever I am below 30 mph (including being stopped) the engine revs every 5-10 seconds. The rev only lasts about a second, but when I am stopped, it actually lunges the vehicle forward unless I am holding the breaks down hard! It revs even when putting it in neutral, or having it parked. I noticed this occassionally a few weeks ago, but after a 3 hr trip today it really became noticable and much more frequent.

Anyone have an idea what could be the cause? Another electrical malfunction?

My father-in-law suggested in might be a malfunction with the cruise control. I would like to see if this is the case, but I'm not sure what fuse to pull. The manual doesn't reveal the location... Any help much appreciated!!

On a related note, I just had the crank case, rear/front differentials fluids changed, as well as the transmission fluid. However, it had the rev issue before that (though not as noticable or regular- also a reason I took it to get the fluids changed out). Additionally, the fuel gauge was acting up (jumping around) about 2 weeks ago- nothing odd since then, however (fuel pump replaced two years ago). I also use the cruise control quite a bit, so I definitely think it could be the culprit.

Check the throttle cable(s)...

I've got a '97 Blazer -2wd, but same engine.
I had the transmission serviced recently & on the way out of the shop, it was idling high & made the "idiot light" come on.
The tech played with the cable about 5 minutes & it went back to normal.
Can't remember what the specific problem was...hope it's that simple for you...
-Mike

Tighten your gas cap. Same thing happened to me last week coming from Florida to Arkansas. I got the lunging idle, SES light, vehicle lurching forward when stopped with foot on brake...yadda-yadda.

Got out, tightened the cap four clicks, restarted. Problem gone. I was in such a rush in my fill-up in Alabama, I didn't do my usual 3-click twist on the cap, it was just "finger snug".
If this "Cheap fix" does not work after you are sure that the tank is closed - the second cheap fix up the chain is to just get a replacement cap for the tank at the dealership or a parts dealer.

It sounds like a vacuum leak with the IAC trying to compensiate. Could be the EGR acting up. Time to put it on a scanner. If you question the cruise control, just unplug the module. It's in the firewall.

Ok, I tried tightening the gas cap, with no luck. I popped the hood and noticed the air conditioner compressor kept trying to engage, and that was apparently the culprit. For whatever reason, the AC is trying to kick in every 5 seconds and it keeps reving the engine for extra juice to get it to engage. My parents actually had a similar problem with their Toyota Camry a few years back- but only when the AC was actually turned on.

Anyone know what could cause this?

I pulled the fuse to the AC and the problem is gone, so it is definitely related....

Thanks!!

Low freon can cause this

Yep...sounds like freon/R-134 or whatever the refridgerant is, is really low.
Solution is obviously to get it recharged and deal with any leaks.

If you're really bored, another way to check it is disconnect the low pressure switch on the back of the condenser & use a smal wire as a jumper to make the compressor stay on instead of cycling on & off. Then you can see how that affects the engine revving.

The compressor comes on with the defroster. And I agree, it's probably a low charge in the system.

Yep...sounds like freon/R-134 or whatever the refridgerant is, is really low.
Solution is obviously to get it recharged and deal with any leaks.

If you're really bored, another way to check it is disconnect the low pressure switch on the back of the condenser & use a smal wire as a jumper to make the compressor stay on instead of cycling on & off. Then you can see how that affects the engine revving.

Great, thanks for the tips. I think this is a good diagnosis. I will probably not tweak with the condenser too much (not that brave!). Come to think of it, the AC wasn't cooling the car down to well torward the end of the summer- I probably should have had it dealt with then. Most likely there is a leak because we had the freon recharged a year ago.

Thanks much!!

I am having the same problem. The vehicle lurches forward when the AC is on, but when it's off, no noticible problem. The Freon Level is normal, and I got it checked for vaccum leaks and everything, so i don't think it's the A/C but it's related to the AC because only when the AC is on does this problem happen. Anyone else know what could be the culprit?