Hello! That Painter Guy here (painting Contractor)

I just bought a 1991 Honda Civic LX (auto 4 door sedan) for a secondary economy car. Engine runs great, no smoke, starts right up
(1.5 engine- PGM-FI) transmissions works great (4 speed automatic) I will try to be as descriptive as possible with the quirks ive run into.

When engine is cold (first start of the day) It starts fine, It Idles fine. Lights off AC off. If i turn on either it drops the idle conciderably.

When reaching operating temperature a couple of things happen.

It idles realy low..like around 450-500 enough to cause shudder. It never dies...just operates very low. It drives fine. Lights off AC off. Turning them both on it will still run but again low idle. 350-400 rpm...

If i drive it on the freeway a bit it will idle fine in D4 around 700-750. City driving it keeps that realy low idle. AC/Lights on or off..

If i shut the engine off, then restart it, if it is hot out..it wont start for a few mins..just turns over. Usualy AC is on when this happens.

If and when it does start...the idle shoots up real high (1500 to 1800) Lights off, AC off. Now if i turn on lights it comes down a bit, if i turn on AC it drops real low then goes back up again.

Makes me feel a sensor or something is amiss...It could be a couple things, ive done some searches but this is got me boogered. Any help appreciated, thanks. Id rather hear the experts then spend a bunch of cash replacing randome things.

 

So some of the research leads to...
AICV =Idle issue
Main relay = Hot start issue-no start issue
Temperature sensor
HITV (cannot find this on my motor)
Should i just replace all these, or has anyone had issues like i described that could point to the culprit.

Keeping in mind, no check engine light has ever came on

 

Idling speed is controlled by an electric valve (EACV, but informally known as the IACV) that lets air bypass the throttle body (since the throttle plate is closed when no one is pressing the gas) and into the intake. They get sticky and / or clogged up, so clean it. It's the part bolted to the top of the intake manifold next to where the hose comes down from the side of the air box. Unbolt it and you will likely see a bunch of black gunk in the air passages. Use spray carb or throttle body cleaner. You don't necessarily need to disconnect the two small coolant hoses attached to it to do that.

With any newly purchased used car, confirm that someone didn't take the bulb out of the CEL. It should come on for 2 seconds and then go out when you turn the key on but don't crank.

 

Ok cleaned the IACV valve, pretty easy to do. I was checking around for broken/bad vacumm lines, wene i seen the butterfly shaft of the carb...facing it, left hand side were the cables attach. The nut had backed off and the cable wraps had walked nearly off the shaft. To the point they were beyond the adjustment screws.
So i slid everything back, tightened the nut. Car wouldnt start

I decided to go for the main relay. Was a 7 pronger. I pulled it and replaced it. Turned on the ignition BANG it started. Shut it down restarted and BANG..seems that issue is solved.

But now its idle is real low..stumbles then it rises to like 3k RPM..wont go down no matter what i do.... I disconnected the IACV dongle and it goes down a little then rises back up, and it does the rise/fall like they mention when its time to clean your IACV valve..great. LOL so i reset the ECU and walked away. (IMaD At this point) IM going to retry this morning and see what happenes. Then i am stumped because it ran before...all i have done is clean the IACV and replace the main relay and fix the butterfly shaft.

Oh and about the check engine light..it does not come on for a few seconds when i turn on the ignition...so i will check into replacing that.

 

First check that the radiator is full. Air in the cooling system will cause erratic readings from the ECT sensor, which leads to erratic idling.

Throttle cable may be too tight now. The throttle plate should be on the stop when no one is pressing the gas. I think the stop screw is a factory adjustment only, but someone may have messed with it of course.

The engine is MAP controlled, so air leaking into the intake from anywhere will simply increase idle speed. It's not like MAF controlled engines where air leaks will generally cause stalling.

Also check that air flow through the IACV stops when you unplug it. Disconnect the hose that comes down from the side of the air box to check, the IACV air flows through it. Unplugging the IACV with the engine running will throw a code 14.

Trouble codes are shown on an LED that is part of the ECU, the LED is always active even if the CEL doesn't work. The LED is found under the carpet on the firewall where the passenger's feet would be. There is no need to install any jumper. Just turn the key on, engine running or not, and the LED will blink out any codes. If it stays off with the engine running, no codes are stored. (Note that it will always give one short blink when the key is first turned on, ignore that.)

 

So just to let ya know what ive done so far..i replaced the IACV with a new one. Brand new. Starting the car (yea it started now) and the idle is a bit lower. More like 1200-1500...much more tolerable.
Originaly i scribed a mark on the distributer, i planed to see if any adjustment would make a difference in the idle..it does not. So i returned it to that scribed mark. (i dont have a timing light)
The car drives, got plenty of power runs exellent with one exception, the idle is still to high. Not 3k anymore...(does snoopy dance) but still a bit to high.
Im going to check what i think is a dashpot valve, i suspect its not functioning so it might be the leak.
I also will check for the LeD codes
A freind mentioned cleaning the EGR valve up, it cant hurt to check it out at least. And i like to tinker anywhoo. Im learning as i go, thanks so far with all the help and will continue to take the advice untill i get it all nailed down.

 

Does yours even have an EGR valve? I think only the California specific version did, those sold in the other 49 states did not.

Again, IACV wires unplugged, you should have no flow through IACV, and idle speed should drop to below normal, barely above stalling out (with transmission in Park and A/C off, putting in gear or A/C on it will likely stall). If it doesn't, air is getting in somewhere-- likely the throttle plate if someone has been messing with the stop screw or the throttle cable.

 

it has what appears to be a EGR, has a plastic peice on top with what i could best describe is two ring clips holding the soft plastic peice over the valve.
Unplugging the IACV does drop idle some but not much. So somewere is a leak i will continue to look.

This is my engine and that EGR is on automatics (mine is an auto)

 

trouble code 14 short quick flashes so...EGR?

 

14 is the IACV code, which is to be expected since you unplugged it.

When more than one code is stored, I think it repeats each one three times then goes to the next one.

to reset codes, disconnect the battery with the key off.