91 DA chugging when started hot, with video

Hey guys,

I had some time off and did a few things to my car. I got it fully tuned up with new plugs, wires, cap, rotor, fuel filter, intake, exhaust, sound system, HID lights, and I took some time and repaired the ICU so now everything works and I reflowed the solder on the main relay. Heres what Im dealing with now....

The car starts and runs great when its cold. If i drive it for more than 10 minutes and let it sit for a bit when I try to restart it, itll og really bad, and I have to bury the gas pedal to keep it from stalling. Itll run like crap and keep chugging until eventually overcoming whatever is causing it, and then itll idle up. It still does the surging idle thing, but Im dealing with stuff one problem at a time. By the way, its a 91 DA with a B18A non vtec, and when it has this idling problem is doesnt turn the check engine light on, and there are no codes to pull when I check it.

Its my daily driver, and id really like to get the bugs worked out so I can finally start enjoying it.
I have spares of pretty much all the sensors, and I have even tried swaping them out one by one to see if thatdd fix it, but to no avail.


Anyone have any ideas?

heres the link to the video I took.

http://youtu.be/9avOEEFNkYo

it could be afew things like the oxygen sensor or maybe your idle air control valve is clogged

The culprit may be the FITV since it may not be closing all the way when your engine is hot.
You may want to remove all three screws that hold it to the IM. no need to disconnect the coolant lines, just take the back plate off and tighten down the ring until its snug, Don't over tighten it, you may strip the plastic if you do.

Also, your idle speed may be a bit low... if you're a complete moron like me, you may have at some point tightened the screw at the top of the Throttle body not having a clue of what it did. lol Otherwise I'm the only moron I know who managed to do such thing.

I tried swapping out a different IAC that I had, and now the chugging stopped but it has the bouncing idle. I cleaned the IAC really well before I installed it, and made sure that it wasnt plugged up on the coolant side. Once installed I made sure that the IAC got good coolant flow to it when the car was started, but its still acting up. I checked the ECU and I still dont have any codes when I jump out the connector. I did remove the intake pipe and make sure that once the car was warmed up that there wasnt air being sucked through the passage that goes to the FITV. I unplugged the IAC and set the idle with the screw, and reset the ECU but its still doing the bouncing idle. The weird thing is that when I unplug the IAC the idle stabilizes. I dont want to run the car without the IAC because im worried itll stall if I turn on the A/C or come off the gas suddenly while on the freeway.

Anyone have any ideas?

The idle should stabilize when you unplug the IAC regardless of it working good or not, that is unless your idle speed or timing are out of whack (which you say are not), but you're right about needing that IAC on the regular.

Check your vacuum hose diagram and check for air leaks, with your engine cold, start it up and spray Carb cleaner around areas that may leak. Make sure the engine is cold though, you don't want that cleaner to catch on fire.

I'm at work now, I'll watch your video later today.

imma chime in here as well. i have a 88 wagon that has the exact same problem. Stuff ive done (not all directly related to the idle problem but just in general) includes a head gasket, cleaning IACV, plugs and plug wires, replacing suspect vacuum hoses, ignition timing, cleaning intake manifold and throttle body. i have no codes and the car runs fine except when hot and at idle. if the car is hot and i turn it off, when i turn it back on it will come on immediately but I have to give it throttle to keep it idling.


just food for thought in the search of the culprit. im still trying to track it down

do a valve adjustment. they might be out of spec.

maybe it could be a coolant temp sensor

Samurai_Blue said:

do a valve adjustment. they might be out of spec.

Click to expand...

and I had a valve job done. had a professional machinest do all new seals in the head and adjust em and had one valve replaced. idk about OP

So, Carmona, does your idle fix itself after you gas it for a bit?

Maddogg, I can only recommend the valve adjustment that the blue samurai suggested.
Come to think of it... I had this same problem before, it was one of the valve cover gasket rings that was leaking oil into Cyl. #2. Check the spark plugs for oil after warming up the engine. (And by that I mean pull them out).

i did the valve adjustment, and its still doin the sam thing. I also cleaned and tightened up the FITV, but alas, its doin the same thing. If i unplug the AIC thr problem goes away, but if I unplug the TP it goes away too. I checked the TPS with my multimeter and at the idle position its reading .37 and at WOT it reads 4.50. It did increase in voltage as I opened the throttle and there were no places where it freaked out or went down. Hmmm. Still stumped.

Just curious, im kinda on the fence in doing an OBD1 conversion. What are the benefits exactly? does it make it easier to diagnose issues, and are there any performance gains if I do the conversion but leave it tuned for stock? Also, I know that I will need to get some adapters in order to convert it, but will I be able to use the same sensors?
The reason I am contemplating the conversion is the fact that My ECM looks kinda funky. It has the tell tale junkyard yellow writing on it and it wouldnt suprise me if some parts of it were starting to go bad.

TeknoStatik87 said:

So, Carmona, does your idle fix itself after you gas it for a bit?

Maddogg, I can only recommend the valve adjustment that the blue samurai suggested.
Come to think of it... I had this same problem before, it was one of the valve cover gasket rings that was leaking oil into Cyl. #2. Check the spark plugs for oil after warming up the engine. (And by that I mean pull them out).

Click to expand...

the idle will settle if i give it gas, but it if I let off, it will go back to doing the same thing. I did have oil but I did a valve cover gasket set as apart of that top end rebuild and it fixed the oil problem but didnt fix the idle.

Maddog, yeah TPS looks fine then, check your battery connections too for corrosion (Ground specially), although they looked hella nice. Any oil on the plugs?
If not, try blocking out the FIT valve with a piece of thin cardboard, same material you would find on a folder but maybe thicker and with a smooth surface. Block off the FIT and give it a test run, reason being: the valve may be locking itself open/close until air is forced through, or maybe the map sensor, it's definitely something that changes when you gas, maybe even your Fuel pressure regulator that gets stuck. Frickin mystery of a century this is. lol

Carmona, I also assume your idle problem goes away after gassing it for a good 1 - 2 minutes, rite? Check your ground cable and battery terminals too.

already checked my grounds and replaced several to be safe. and the idle problem wont go away permanently or even temporarily. as i said, if i hold the throttle it will idle ok, if i let off, it goes back to surging. i also checked my FPR and that was fine

well....

I have had a stable idle the past few days. When I come to a stop itll sit right at 800 rpms, but now I have a new problem. I dont think that the other IAC that I swapped in is working. If I turn on the cabin blower the idle drops to about 500, and if I turn on the A/C compressor itll drop to about 200 and try and stall. I dont think that the IAC is adjusting to change the air being let into the intake manifold. When I hook the IAC to a battery, itll click and I can see it move back and forth. Another weird thing is that if I unplug the IAC and plug it back in, I can hear a change in the intake hiss sound but the idle really doesnt increase, and even stranger, if I unplug the IAC valve and turn the idle screw on the throttlebody, the idle wont climb above 900 no matter how far I back the screw out.

One more thing... do I still need the air boost valve hooked up? and what purpose does the little assembly right by the dash pot that has the air boost valve do? It has a 5/16 inch vacuum line that goes to a connection on the back of the intake manifold.