Idle fluctuates between 1000 and 2000 rpm

I have a Honda Accord 98 180,000 miles. I recently cleaned the EGR valve track on the manifold. After I put the car back together I have the idle fluctuating between 1000 rpm and 2000 rpm. I have scanned the intake for vaccum leak but have not found any. I have double-check the electric connection, the and the vacuum hoses, all ok. I just read that I may have bubble on the coolant which could be true, I’ll do that tomorrow, but could that be it?. I have all new gaskets for the EGR valve, and plum, and went a little farther with the torque for the plum ( 240 in/lb as opposed to the recommended 192 in/lb). What am I forgetting to check ? I had the EGR problem for a while, and I was glad to finally get at that problem, the intake was clogged up with carbon residue. But this new problem is worst. I still have the EGR problem showing on the computer with a new code (P1491 & P1498). The old code was P0401. I have tested the EGR to make sure it opens and it works, the EGR valve is less than one year old since I have attempted to fix the EGR problem before with limited success.

Thanks for any help.

Do not know about honda but on toyota it would be idle air control valve

Those codes point in the general direction of the lift sensor - it monitors the actual operation of the valve. So the valve itself might “lift” but the ECU doesn’t “know” it - or is getting mixed signals about it. I know you checked the vacuum lines, but I would do it again. In fact, I’d be tempted to not bother checking them and instead just run new lines - its cheap. In addition, make sure that the port that provides vacuum for EGR operation is not clogged.

If you don’t find anything there I think that you have to start shooting the electricals. For that you’ll need a decent repair guide that provides the specs for the sensor and other system components, and a decent digital multimeter.

It sounds like a vacuum leak. Over-torquing is not a good idea at all. You may have warped something, causing a vacuum leak.

The fluctuation stops once the car warms up does clue ignites other recommendations ? . I have a Honda repair manual and have tested the EGR as far as what the manual recommends. The next thing I will try is cleaning the IACV as hd72mm said, and refill the coolant just in case. I’ll do the hose thing after that, although I have sprayed the intake with carb cleaner and scanned the intake with an ad-hoc stethoscope and no leak was found.

Spraying Throttle Body Cleaner into the air intake tube to clean the intake tract, and the iacv, is a good idea. Of course, the TBC is injected AFTER the MAF (Mass Air Flow) sensor. On the MAF, use MAF cleaner. Any of these things could help; but, there are no guaranties.

Thanks for all the comments. I tested the car starting it cold, and the idle fluctuation is gone. The theory was to allow the valves to work normally and become unstuck if they were stuck after the cleaning. Whatever it was, it is gone. I put 40mi on the car to see if it would adjust to the changes after I had cleaned the intake. I still have the check engine P1491 & P1498, I am thinking it may need a dealer to reset the codes, or put more miles in the car to allow the new reading to override the old ones. I’ll make sure to post how the check engine number cleared.