This is kind of bizaare but when I start my car (cold) and then shift into neutral, the rpms rise and fall continuously. But, after the car has been driven a bit and is warm, the problem doesnt occur. I'm thinking maybe a vacuum problem because my cruise control also has a problem- it won't engage unless I press the "set" switch and then the "accel" switch. Shouldnt it engage by just pushing the "set" switch? And then, after it does engage, about 5 mph bleed off until the car accelerates back up to the speed i had originally selected. Maybe the 2 problems are not related at all but it sounds kinda fishy.

91' accord 2 door lx

 

the 2 problems are not related ,, on the idle surge,, chk the inner part of the fast idle valve,, remove the 2 phillip screws at top of fast idle valve , get a big screwdriver and tighten the inner valve ..

as for the cruise loosing a bit of speed try to make sure cable is adjusted properly

if you set the cruise at 40 mph and push the set switch, ceuise control should stay at 40 or there about a slight drop might be normal in some models
cruise will not raise the speed till you push the accell button

 

Cold idle surge; be sure the block is full of coolant and burp the block thru the 12mm bleed screw at the T-stat housing.

 

Thanks for the info, I'm going to flush and fill my coolant system since I need a new t-stat anyway so I'll try that 1st. If that doesn't work I'll try Desert's suggestion. I should also have noted that the car had been sitting for a while.

 

That fixed the cruise control problem; just needed to tighten the cable- thanks desert

 

what about the idle surge ??

 

The idle surge seems to have disapperaed at least for the time being. I checked the fast idle valve and its working properly...i also did a flush and fill because I had a bad t-stat. Hopefully it wont return!

 

I have a 98 acorn v6 that rpms fluctuate between 1000 to 2000 at idle and no dtc code .I replaced the iac valve at about 90k it now has 160k. I disconnected connector from the iac valve and it did the same except at a slower pace. Is it possible it can be another bad iac valve or maybe a tp sensor.? It just got back from the tranny shop(overhauled) Should I kept running it to see if I get code

 

If it's surging while the IACV is unplugged, then look for other stuff first.
Vacuum leaks?
Air in cooling system (really)??
Throttlebody bore & throttle plate dirty?
Accelerator cable has to go slack, so throttle can close completely?

 

Will do.thanks