Hello.
I am new and hope some can help. I searched many thread but wasn't able to find exact symptom.

I have 98 civic LX sedan with D16Y7 engine, since last year, when weather is warm or I am in middle of slow traffic for while, my engine RPM surge to 3,000 range and my car wants to move even with brake.

So far I checked for vacuum leak, cleaned IACV, bleed coolant & cleaned throttle body, many remedy I found from this forum.

My coolant temp. gauge is normal and coolant is full on both radiator and reservoir (I used Prestone brand instead Honda).

Any suggestion would be greatly appreciated.
Thanks.

 

The only way for an engine to make that much power is for air to go into it. Thus there is a way that too much air is getting into the intake. Maybe the throttle plate or IACV doesn't close fully, or there is a vacuum leak. For example the brake booster could be leaking. Also check the FITV if there is one.

 

MK378, Thank you so much for your suggestion, and I will check all the suggestion you wrote.
I am pretty sure throttle plate fully close and IACV is clean, I will check for any air leak.
My car do not have FITV.
I noticed my radiator fan do not seems to turn even I wait for while with AC on, I swapped radiator fan relay with other (AC condenser) to see it makes any difference, it still looks like it start to run, then connected fan itself to battery to see if it is functional and found it does work fine.
Could radiator fan not function cause engine to surge? when warm day? My temperature gauge remains in middle even during warm day or slow traffic.
Thanks in advance.

 

After many days of finding, I replaced IACV, bought used one, cleaned very well and installed, Still same problem.
Finally, I went to local mechanic who I was supposed to be really good.
He looked and adjusted throttle cable lock nut, there was little tension and I guess it was not fully closed during idle and when car was warmed up, that little opening caused my high RPM.
It only took him less then 2 min. to find.
When I did head gasket replacement job, somehow cable tension got tightened. All this time, after changing IACV, coolang temp. sensor, replacing coolant I overlooked cable tension.
Thank you all for helping. E****ially MK378.