PROBLEM DESCRIPTION: Ok, so whenever I run my car hot (at least 30-60 minutes) the RPM tachometer starts going haywire. The RPMs will be at 3,000 while i'm on the highway, and then instantly fall to 0, and then surge back up to 3,000 again, and then repeat. It honesty look as if the RPM tachometer is possessed! And it feels like my car is having minor tremors and seizures. When the tachometer surges like this, the car lurches violently.. it almost feels like a car running out of gas on the highway (we've all been there before). It's to the point where I'm afraid to drive it excessively for fear that I will damage my timing belt, or jump a tooth! If I'm only driving locally (i.e. 15-20 minutes), then it's perfectly fine. Drives smooth as butter. I've noticed though, that whenever I drive for long periods at night, or during overcast/rainy days, the problem is less persistent (or non-existent). It's even to the point, where if I'm driving constantly with the sun on my back (and not on my hood) that the car drives without this problem. So I'm almost 100% positive that hot days and heat are aggravating the problem...whatever it is.

BACKGROUND HISTORY: So I've been putting a lot of miles on my 96 Accord lately. I've had it looked at (and test driven) by two separate mechanics, both of whom didn't charge me anything because they couldn't properly diagnose the problem. They were especially baffled (and I as well) because the violent RPM surging hadn't caused my ECU to trip off the CEL. One of the mechanics claims that it's definitely electrical and that the reason the CEL hasn't tripped yet is that it's intermittent and doesn't occur at intervals long enough for the ECU to catch it. Is this true? Also, it started acting up and doing this the SAME day that uprooted my middle console and took out my old radio unit and replaced it with a nicer CD player. Could it be some faulty wiring or a short in my electrical unit? The first day my car began doing this, it was stalling out while driving at high RPMs on the road. It was cutting off at normal parking idle after a minute or two of parked idle. I found the problem was that one of my spark plug wires was not properly attached the spark plug in the front engine plate. I thought I had fixed the problem until I drove 10 hours from Colorado to Oklahoma.... That's when it got REALLY bad. I had to drive for an hour, park it in the shade for 10 minutes, and let it cool off, and then get back on the road and try for another hour of drive time.

POSSIBLE PROBLEMS: The same mechanic that claimed it was electrical said that he's sure it's something in my distributor cap.. and that the culprit is probably my camshaft position sensor. I'm almost positive it's not a fuel or air issue. The fact that it's so intermittent, and dependent on outside temperature makes me think it's electrical. What do you guys think?

 

Almost sounds like the ICM in the dist is going. I've heard that some places can test these, you'd want them to run the tests several times as it sounds like it is giving up when it gets hot.

When it does this, can you check for spark at the spark plugs?

 

It usually only does this when I'm driving (and at higher RPMs).. so no, I don't know how I could test for spark? So if the ICM is in the dist cap, would it be cheaper (and easier) to just buy a new dist cap? I saw one on autozone for around $20, but the ICM was $50. That doesn't make sense. How hard is it to change out the ICM from the dist cap?

 

The cap and Ignition Control Module (aka Ignitor) are two different things.

The ICM is under the dist rotor...see pic, this is for the "internal coil" dist which I'm pretty sure the EX used.

If the cap and rotor are due for a change it can't hurt to go ahead and replace them and see what happens - they are maint items and wear out.....or at least inspect them.

What has me thinking the ICM is that one of the wires from it actually feeds/signals the tach inside the car - the blue wire if you care . Again please remember all I have to go on here is your description of the issue.

Edit:.....forgot the picture

 

Poorman212, I can always count on you to try and help with my car questions.

Ok, so another thing I noticed today is that when parked and the car idling, the A/C performs horribly and doesn't blow out cold air. When in motion, the A/C blows out cooler air... however, when parked and idling, it seems that the A/C really puts a huge burden on my car, and I can see the RPM gauge occasionally drop, and feel the engine sputter like it's about to stall. IF I turn the A/C off, the engine idles fine. Is this also a problem that is caused by the ICM?

 

Nobody else has any advice? Any thoughts people? I need some ideas before I start throwing money at this problem...

 

The ICM (aka igniter) is a good place to start, for your generation Accord, for 4 cylinder engines the tachometer drive circuit receives pulses from the ignition control module (ICM) in the distributor assembly; whereas for V6 engines the tachometer drive circuit receives pulses from the ignition coil.

The ICM may be the cause for part of your issues. The A/C problem may be a separate issue. Take care of one issue at a time, if it solves other issues, so much the better. As was previously mentioned, a few auto parts shops can test them for free. So, if a parts shop can test the ICM for free or you test it yourself, you wouldn't necessarily be throwing money at the problem (at least not blindly) as you have performed tests or at least narrowed down the possibilities.

Here is a link regarding some ignition troubleshooting:
Honda Acura ignition (no spark) troubleshooting tutorial - How to

 

Thank you Sir - yes I was assuming this is a 4 cyl engine.

OP - can you confirm the engine, 4 or 6 cyl?

 

Yes. It is indeed a 4 cyl. I bought a ICM chip from Autozone today for $123. Is that too much?? Also, when I called on the phone they said they could test my ICM.. When I arrived the next day however, there were some young kids working there and they were scratching their heads when I asked. I bought the chip anyways and figured I'd take it to a mechanic and have them test it when I find the time.

For the record, I usually like to do things myself and reduce cost, but I"m currently working/living on an oil rig out in the middle of nowhere, so I don't have the voltage meter, tools, or garage to really fool around with it..

 

Ouch.....but I understand the situation......not trying to make you feel bad, I'd bet a bone yard would sell the dist off one of these for less than that. Are there any around where you are, you could try "www car-part com" and search the area.

I hate to have suggested you spend money without proper testing.