Rough at idle.
 

Ok. I do believe my car is running rough at idle. My car starts up quickly each and every time whether its a cold or warm start.

After a cold start the idle is very rough. Fluctuates up down from 900+ down to an almost stall. From this state I just start driving.

Once I have driven and the engine is nice and hot,... the idle jumps up and down from 900 - 1000.

Warm start its the same,... up and down from 900 - 1000.

Driving is awesome though. Seems fine while driving. Sounds nice and drives nice.

One thing I have noticed though,... the exhaust smells bad. Maybe an unburnt fuel like smell?!?! It's very noticeable. I was showing the car to a friend and she noted, "Geez the car smells."

I am thinking that maybe the car is running rich. It's been a long time since I been in the 944 game. Very rusty at this. And for sure I dont know 951's.

I did a search and learned of a few things that could cause this. The idle stabilization valve, vacuum leaks, and bad O2 sensor. Whatelse?!?!

I read that the hoses to the ISV usually are cracked? That is can be cleaned? that its under the intake?

Any particular vacuum hoses I should definitely check out?

How do I test the O2 sensor to see if it's bad?

Any other suggestions? I had to replace the hose to the power steering pump reservoir because it was cracked and leaking. Wouldnt be surpised if if there were others.

Thanks guys.

It does kinda sound like a vacuum leak. But you never know.

How about the engine temp sensor? If that was bad, it could also cause the engine to run rough at idle when cold.

Clark's has got procedures for testing most everything: http://www.clarks-garage.com/shop-manual/elect-19.htm

http://www.clarks-garage.com/shop-manual/ts-01.htm#cold-idle

As to the hoses, I'd just try and tighten every hose clamp that is accessible, at least first.

The balance of the vacuum hoses are under the intake manifold - which is pretty easy to take off.

But what about the more mundane things like your plugs and the rotor and cap? Cleaned and gapped your plugs lately? Doesn't cost anything to do it and it might help.

Well,... the PO said that everything was new and taken care of but to be safe I will start with the simple things first so atleast I know what everything looks like.

I will check clarks-garage out. You know,... I do remember the PO saying something abou the ISV. He said he didnt mount it. That its laying under the intake manifold wrapped in some kind of plastic something. Hmmm. I'll keep you guys posted. Take some pics of everything too.

LOL - the ICV is laying under the intake wrapped in plastic???

The ICV is pretty important at start/idle - I'd suggest you get that sorted out before anything else.

The ISV looks very new. the portion I can see. very clean looking. It is wrapped in some kind of orange thermo resistant plastic something,... I will get a pic of it later.

Ok,... I talked to the PO about the surging idle/ shudder. He said the ISV is brand spanking new. Got it in march. He said he pressure tested the intake and found air hissing out of the ISV and the throttle body. So thats when he bought a new ISV and cleaned sealed the throttle body. No intake leaks after that. The O2 sensor and temp sensor are also new within the last 2 - 3 years.

He said that it might be the 65lb Delco injectors. That they might not be good at metering the small amount of gas at idle. He said he has the original injectors that he had professionally serviced and flow tested. He was going to eventually sell them but he said if I want to swap them back into the car i could that. He said I would still be able to maintain the same amount of boost which he said was 15psi but it's actually 16psi. But the original injectors would be at their max duty cycle where the 65's would be at a low duty cycle.

What do you think? Could this be the case? If so I dont know if I would want to swap them out because the injectors would be maxed out everytime I floored it. There has to be a way around this. Also I dont want to swap them out to still have the same problem.

What do you think? Whats the size of the stock injectors? Anyone out there running 65's? Something else other than the stock injectors?

i'd use occam's razor here

the idle can bounce around a bit with a worn rotor and/or cap - that is the sign for me to change mine - i only get about 10-12k miles out of mine before it starts to show signs of wear - yes the car still runs at that point, and would for quite a while, but the idle is not as rock solid

Forgive me,... occam's razor? I will check my cap and rotor now. Thanks. Any more suggestions would be appreciated.

google it - very famous philosophy

Ok I read it but im lost. What would the entities here be? So,... basically it means that people make things out to be more complicated than it really is? Or,... everyone has their own answer or opinion on something that already been answered/ explained? Both?

How doe that apply here? It's probably something more simple that the injectors?

the simplest answer is likely the correct one

very basic philosophical principle, i think taught in every high school, and definitely in basic college philosophy

we tend to over think things way too often, especially on these boards

LOL. I am guilty as charged! LOL. I hope my girl doesnt see this because she will definitely chime in on it. I will check the simple things first. When I get a chance though. I have a lot going on right now.

I have been experiencing some small misfires out the exhaust too when changing gears and once tonight when I down shifted to second and slowly got off the clutch to drive. I am not the best when changing gears with this car. Im still trying to get use to it. Most of the time Im not giving enough when I come off the clutch.

Hi all, new to the forum......I have the same problem, similar anyway. I have replaced my coolant temperature sensor which smoothed things out quite a bit, but once the temps are up I get the dreaded idle bounce again! It varies between the hot and cold idle speeds, give or take a hundred RPM or so. It doesn't almost stall.

I'm thinking that I need to clean the idle control valve, but i don't really want to remove the intake plenum. I have a long history of simple jobs becoming not-so-simple, and this has the stink of something bad happening.

I did the propane gas vacuum leak test, all seems well. Did the water spray at night test, found a small short and fixed that as well.

Any other ideas?

The hose going to the ICV from the intake manifold,... clamp it while the car is surging the way it does. If it idle stablizes then you need a new ICV or you need to clean it.

You can also check your plugs and cap and rotor.

Regarding Occam's Razor;

Many years ago I had a Chevette. The Chevette needed a rear brake bulb. I went and bought a package of two. I put one in, no light. I put the second one in, still no light. Assuming the worse I get my brother up from the city with his multi tester, we start looking for a wiring problem, checking grounds, pulling fuses, cleaning contacts.......still no light. My brother, by now very frustrated, takes a close look at one of the bulbs- it's broken inside. He checks the other bulb- ditto. That's when I learned the value of Occam's razor as a valid approach to problem solving!!

LOL. Thats quite funny. Well,.. not only does my car have a surging idle,... the exhause smell is pretty bad too. It does smell liek fuel. I even smell it when driving. if I come to a light with teh window down,... I smell the exhaust.

Now im aware that if you go to get gas and fill it up,... that you will get a strong gas smell inside the car after some moderate driving. Thats fine. But this smell is a different fuel smell and exhaust fuel smell. I dont know if turbo do this normally but I dont know. I am goign to check my cap and rotor, plugs etc within the next fews days. We'll see.

exhaust smell is an entirely different deal - cap and rotor won't generate exhaust smell

while there could be more than one thing going on at the same time, sticking to the idea of the simple first, it could be a toasted O2 sensor

It will if you put fuel into it.

lol - yeah, but then there are those pesky flames to put out