User 52121

Alright... in a several-month quest to iron out some little issues with the car, only two remain and they seem to be the kind of stupid little issues that just laugh at me. 135k on the car, it's an '86 951, mostly stock motor-wise aside from Weltmeister chips, a LR boost enhancer, and a 3" exhaust w/no cat.

1- Car runs GREAT when cold for the first ~5 seconds. Then idle gets funky and inconsistent (drops down to ~600, stumble stumble sputter sputter then jumps up to 1400, nice and smooth, then drops to 600 again with more sputters, then back up to 1400, the finally settles in around 1200.) This behavior is consistent with every cold start. Even the 5 seconds thing.
2- BAD hesitation until car really warms up. Getting worse as the temp is dropping here in Chicago.
3- Hard to start when warm. Not hot, but warm. Hot restart (within 10-15 minutes of running hot) car fires instantly. But if the car sits for 30-45 minutes I've gotta crank the daylights out of it to start.

My question to the group: Is it possible that a bad ICV could cause these three issues?

Cliff's notes as to why I'm leaning towards the ICV as the root of my evil:

Jumpered the two pins in the diagnostic port to set the idle this morning after cleaning the TPS (also learned after some deep reading last night that idle should be ~850, and my car has always idled around 1200.) Car was cold from sitting overnight. With the pins jumpered, car started, and aside from running a little rough at 600rpm or so, idle was consistent and stable. I attribute the rough running due to the fact that the car was cold and wasn't being compensated properly (which is usually the ICV's job.) As soon as I un-jumpered the pins and restarted the car, idle was erratic and all over the place like it usually is when cold. I didn't drive the car with it jumpered, but could tell just from blipping the throttle while in the garage that the car as MUCH more responsive. Unjumpered, when it's cold, a blip of the throttle usually results in a sputter instead of a rev.

Longer version (skip if you don't care):
I've been chasing both this warm start and cold hesitation pretty much since I brought the car home in June. Car runs like a champ when fully warmed up (aside from the hard start issue.) I've gone through it over my ownership so far taking care of little things... some regular maintenance, some stuff that was obviously just broken, some "just-in-case" or "while I'm in there" things, and a couple that I thought might be the problem.

Stuff I did to try to fix the warm start issue:
- Replaced fuel pressure drainback valve
- Replaced fuel pressure regulator
- Had the injectors cleaned and flow balanced

Stuff I did to try and fix the cold hesitation:
- Replaced DME temp sensor
- Cleaned the AFM (it was dirty, car definitely runs smoother now)
- Cleaned the TPS (car now idles at 900 instead of 1200 like before, so this WAS a problem)
- Installed all new vacuum lines and venturi delete
- I also did the "failing HG test" where you run the car hot, shut it down, relieve pressure in the cooling system, then let it cool overnight and see how it runs in the morning. No change to cold start behavior.

Stuff I replaced as either "while I'm in here" or "crap I just broke that":
- New fuel lines, replaced all 3 with the snazzy Lindsey ones
- New fuel filter
- New reference sensors (broke 'em when trying to remove from the bracket after connectors crumbled)
- New fuel pressure damper (popped the internal seal when attempting to remove old fuel line in vise)
- New plugs (NGK BPR7ES)
- Disassembled and cleaned the ICV (didn't know/think it was a suspect at the time, just figured it'd be a good idea to clean it)

I have a new O2 sensor in the box sitting here, as this was my next guess (albeit unplugging the O2 sensor didn't change cold start behavior at all.) It was suggested a few times as the possible culprit in other "hesitation" threads here on RL, so I figured I'd give it a shot. But after jumpering the pins, disabling the ICV, and seeing the difference in cold idle... this is definitely a problem. Just not sure if it's THE problem, and am curious what others think. Based on my knowledge, I'm inclined to believe that it could be it - though it wasn't my first (or even second) guess.

tyro

Just bend over and buy a new one already!

Here's my experience with the ICV:

https://rennlist.com/forums/944-turb...-86-951-a.html

odb812

my car ran the same way with a bad ICV. I shorted the pins on the diagnostic port as you did and left the jumper in there ever since. When I get around to taking off the intake manifold and removing the cycling valve, I'll either replace or remove the ICV. The car has been running fine with the ICV disabled on the diagnostic port, I just raise the idle when it starts getting cold and lower it in the summer. I even drove it for a while with the ICV disabled and the O2 disconnected and it was fine.

User 52121

Hahaha!

Yeah I actually ordered one this morning when I went to pick up my O2 sensor. It'll be here tomorrow. (Local parts place can get Bosch parts, usually for less than listed on Pelican, and within a day. Sweet.) I just wanted to know if others agreed that it could be the culprit.

I guess tomorrow night I'll just dismantle the whole dang thing again to put the new ICV in. While I'm in there might as well swap out the O2 sensor (unless it looks to be a total bitch, then I might wait.) Have a brand new coolant recovery tank to put in too since the one that's in the car now looks a little balloon'ed.

tyro

Why are you replacing the O2 sensor? For fun?

Do you have a wideband gauge on the car?

User 52121

Doing it because I already have it in my hands so I might as well.

No WB02. Don't need it. I let the DME/KLR control the boost, all I've got in there is a boost enhancer. I'm not messing with any tuning, don't really want any more HP out of this car. It's quick enough to be fun, and since I plan to use it mostly for auto-X, DE's, and as a fun street car, I'd prefer it to be reliable. I know from experience: once you start modding for more power, you start to lose reliability. I've had my fun going fast in a straight line (11s in my old Talon, 11s in my old Z06, 13s in my old Omni), now I want to have fun in the corners

tyro

No problem.

If you had one, you could easily tell if the O2 sensor was bad.

I don't really use it for "tuning" as either of my cars are not all that hopped up, but I found it to be a useful tool to diagnose normal operation. I found it hard to justify not having one considering the new AEM UEGO gauges are $218 at Summit.

Did you get the ICV installed yet?

TRP951

Check your wiring under the boots when I looked at mine two wires were completely frayed and shorted out.

User 52121

I hear ya. At some point I will probably get one for the same reason you listed. Plus it's never a bad thing to have too much information. I just need to come up with a creative place to put the gauge (along with a boost gauge which I don't have yet either... thinking of stashing them in the glovebox somehow.)

No ICV yet - should be here around noon. I'll run up to the parts place to pick it up at lunch, and will tear into it tonight after work.

I know for sure the ICV is causing the cold hesitation though. I stuck a jumper in the diag port this morning and ran out for coffee. Aside from having a hard time idling (until the car warmed up), the hesitation was completely gone.

I'd also swear the car seemed to spool up a bit quicker... but that doesn't make a lot of sense, and I couldn't really beat on it anyways since it was raining. But the car seemed to be a lot more responsive. Probably placebo - I'm really good for that.

minho78

Well let me explain my rough idle fix. I had a rough idle at start up for about 1 to 2 min. It sounded like it was runing on two cylinders. I had this problem for the last 8 months I was going to buy a new ICV also. Then I thought about it and this symptom started when I replaced the TPS 8 months ago. If I would pull the accelerator cable just a littlebit the car would run fine. So I adjusted the TPS to click and the problem is gone. My .02cents.

Please let us know the outcome.

User 52121

Well I got the car back together - did everything but the oil change. New ICV, new O2, new coolant bottle. Fired the car up this morning, and she fired instantly and settled into a 1000rpm idle. It's NEVER run this smooth before when cold.

Unfortunately I didn't drive it until the car had warmed up a bit (I was making sure I didn't have any leaks anywhere while the car was running in the garage) so I don't know for SURE if the cold hesitation is gone (but I'm fairly certain it is.) I'll run out for lunch in an hour or so and see if the warm start problem went away.

tyro

Good news!

Take the old one apart and check for obvious wear..it made me feel better when I found mine to be rather worn.

Let us know how it goes when it gets a bit colder..

User 52121

Cold hesitation definitely resolved. Warm *start* issue resolved. Fires right away when warm, no ridiculous cranking. But promptly stalls after she fires. Have to fire it, blip the throttle briefly, then she settles into an idle.

For now I'm just going to deal with it. Only have a few weeks left before she gets parked for the winter anyways. After that I'll probably clean the electrical internals on the AFM and possibly just throw in a new TPS. *shrug*

tyro

I assume you set up the idle properly after installing the new ICV?

User 52121

Yup.