Rep Power: 0

for the past couple of weeks noticed my rpm needle would go up and down while the car is one and on park, give or take between the 1&2. Usually does it when the car is warm and has been running. Wont do it when Im holding the brake. Runs great. I just recently had the mechanic try to solve this issue. He changed the Throttle Position Sensor. drove it for about 60miles and the problem was still persistent. now however, I smelled a mild burning smell coming from the engine. no smoke or anything. had him come back out today, he removed the IACV, he cleaned it said it had A LOT of black dirt/grime on it. I drove it for about 5mn and it ran smooth. 1hr later, I go run an errand the rpm needle was very mildly still going up and down between .5-1. However nothing like it was prior, still noticeable and can hear the engine as if i was lightly revving it up. I also did get this noticeable coolant aroma emitting from the engine. just recently had an oil change, a tune up about 3mos ago. I do very little driving about 150miles each week. Id say about 80% of the engine is still all original. Can anyone shed some light on whats going on with my little Civic?

 
Rep Power: 234

May need a new IACV, or you have a vacuum leak (I would start with checking the vacuum hose going to the brake booster), or a possible bad headgasket.

 
Rep Power: 0

Take off the radiator cap, start the engine, see if you have bubbles. Easiest way to see if the gasket is blown. ANd if youre like me you want the costly issues excluded first

I had a similar issue with idling and near stalls but after I heavy duty cleaned the IACV and got air out of the coolant lines it was just fine. Air in the coolant isnt too uncommon, and the IACV on these damn things is a common issue too.

 
Rep Power: 0

What's an IACV, I have the same problem.