My 93 Honda 2.0 liter accord idle jumps up and down between 800 rpm and about 1200 rpm when hot. I double checked all the vacuum lines and cleaned the idle speed controller. No check engine light. Help?!
My bet would the coolant temp sensor. Your service manual should have a list of expected restistances/voltages for certain temperature ranges that you can check your sensor against with a VOM meter.
The previous generation Accords used a Golbergesque idle control system that had a computerized control valve and two thermal valves a bunch of vacuum tubing, but I’m not sure if that was still the case by '93.
The ISC has no vacuum lines just the two coolant hoses. I can check the coolant temp sensor with my VOM. thanks for the tip.
How did you check for vacuum leaks? B/c that just sounds a lot like a vacuum leak, and many are notoriously hard to find. Did you put a vacuum gauge on it? Also be sure to check the intake manifold for leaks - and clean the throttle body.
I did a visual inspection and removed some of the vacuum lines to check the sides I couldnt see. How much vacuum should this pull at a cold idle around 1000 rpm? Also I cleaned the trottle body about 200 miles ago it was very dirty and made it run alot smoother but didnt fix the up and down idle. What about using a propane torch to check for leaks???
My favorite method is the UNLIT (obviously) propane torch. I rig up a piece of flexible hose that is easy to fish around. There should be a schematic of the vacuum system under the hood that you can use as a guide to make sure you get it all, but don’t forget the intake itself.
The best way to know what the vacuum ought to be is to know what it is when the car is running normally. This is b/c it will vary a bit by engine and also by altitude. Standard vacuum gauge guides will be given assuming sea level, but the rule of thumb I have seen is that it will drop an inch Hg for every 1,000 feet. I am at about 800 feet and my normally running engines pull 18 inches. The typical range that is given as normal is about 16-22. Slap one on and report what you get along with your altitude.
Thanks, I will try this in the AM and report back. Our altitude is 1500’.
It looks like the coolant temp sensor is the culprit here, it read 0 ohms regardeless of temperature. I had to order it. I will report back Friday 3-19-10.
Correction— the ohms were infinite, or an open circuit at all temp ranges.
Still need help. The car does excactly the same as before. the idle jumps up and down when hot, it pulls 16 in. of Hg hot or cold. I changed the temp switch also. I tried for an hour looking for leaks with a propane bottle but could not find anything, I did notice when I pull off a vacuum line the idle went alot higher when it oscillates. Help please.
I did a vacuum test on the egr and it does not hold, will pull it out and check it again.
Scratch that it does hold vacuum, but does not stall the engine when vacuum is applied. While disonnecting hoses’ and looking for leaks I did notice when I disconected the # 21 vacuum hose that goes from the TB to the MAP sensor. the engine stops porpising. Then If I apply a little vacum to the hose it idles normally. I checked the vacumm port on the TB it has about 10 in. Hg on it. This port has the very small inside diameter. So now what??