911_pilot

Like many 3.2 engines, mine has a rough idle that gets a little smoother when warm. This "better running when warm" has been in the summer Texas heat.

When I have the "closed throttle switch" connected, the idle is very rough and the engine attempts to idle around 500-600 RPM, and will then rise to 1000-1200 RPM then back to 500-600, before finally settling down to 800 or so RPM. This takes a full minute for the engine to settle down and quit hunting.

When I disconnect the "closed throttle swith" connector, the engine idles at 900 RPM and does still hunt a bit but not nearly as much, and perhaps for only 30 seconds or so. So, disconnecting the "closed throttle switch" makes a difference for the better. With the switch disconnected, and the engine is at full operating temps, I occasionally have the engine idle at 1200 RPM for maybe ten seconds when I come to a stop. If I wait for a few seconds, the engine will idle back to a fairly steady 800-900 RPM.

There is a lack of power at idle speed RPM's and when leaving a stop and I need to raise the RPM's to 2500 RPM or so to have a solid takeoff. I don't intend to lug the engine, but there should be good power response at 1500 RPM.

At freeway speeds of 2000-3000 RPM or better (while under load) the engine runs excellent, lots of power, steady rythym, and does not hesitate when needing to pass in fifth gear. All the way to 6000 RPM the engine runs excellent.
I have not exceeded 6200 RPM.

What's been done.....

The usual (physical and visibile) vacuum leaks are corrected, new idle control valve, adjustment to factory gap specs on throttle butterfly, all electrical tests are in range. Oh, and a valve adjustment plus new 02 sensor. I have not traced the vacuum line to the brake booster. All of these small fixes have made the engine run better a little at a time.
The vacuum leaks being of course the big fix. All hose clamps are tight, and double checked. I have also sprayed WD40 (using a heavier liquid) around the base of the intake runners to check the intake gaskets for leaks. Did not find any. The correction that made the largest betterment was finding that the small vacuum hose from the back of the throttle body to the Warm Air Regulator was disconnected. The rubber had swelled and the hose had flallen off, or bumped off and not discovered by the PO. A fresh cut and a tight fit made a BIG difference of course.

For a while I have suspected the CHT sensor or the Warm Air Regulator as culprits. I have heard of no test for the WAR as it is vacuum controlled. CHT ohms are in range. I do know that the CO is slightly out of adjustment on the low side. So the engine is running a bit lean. During the June emissions test for renewal of my inspection, the test showed 0.0 and 0.1 CO on two back to back tests with engine warm.
Dead stock engine, very tight, normal oil useage. 73.5K on the clock.

Here's The Odd Part.....

Last weekend the air temps dropped into the mid-forties here in South Texas.
On starting the engine, to my surprise the idle was perfect. Up to 1200-1300 or so for fifteen seconds (+ -) and idled back to 900 or therebouts and off we went. Ran absoutely divine until the engine was warmed up (at first mark) then back to the slightly rough idle. I was able to allow the engine to idle at stop and let the clutch out to begin rolling...to my amazement the engine had a ton of power off idle and did not require the usual goose of the throttle to begin rolling. This is really stumping this garage mechanic (me) who thought knew something.

To make this condition a bit more pleasant I run around with my "closed throttle switch" electrical connection disabled. This allows the engine to run much better overall as mentioned above. Basically I am 'fooling' the DME into registering that I have my foot slightly on the throttle at all times.

I have pretty much dog-eared my Bently Manual in the Fuel Injection Section.
I am missing something here. The cold made the engine idle/run perfect...until it warmed up.

Okay, engine gurus....can someone point me toward North?

911_pilot

J. Brinkley

thats the best description of a problem that anyone has ever written.
once you fix all the un metered air leaks I would think the next thing to do would be check the idle AFR.

o2 sensor,chip, and off idle switch. are the most obvious things affecting idle rpm, I mean other than mix being off, or idle speed itself off.
one of the best tools I've used the most is a wideband meter, as you alter/fix stuff it is important to keep the afrs in the range. This wildly affects idle.

one other thing, I notice very little difference between 100 degrees ambient and 40 degrees. I don't use the stock o2 or the air reg. I do know that a bad, or failing cht might still let you car run/start, but when warm, a bad cht will make the engine die. Even if your VM says it's good, it still could be dead.

Rick K

I was having similar issues (kind of) with my 84 (mine is a RoW). When cold, the car would buck pretty aggressively at low RPM range and idle was low - car was not happy. Replaced the head temp sensor (the one in there was original - and that version hasn't been made in over a decade and is inferior in design)...and that helped smooth out the bucking, but I still wasn't happy w/ low range RPM performance. So we tried disconnecting the O2 sensor - but the car was REALLY not happy, which was odd - usually that makes it happier.

I talked to Steve Wong about getting a chip for the pcar - and he said b/c the car is euro-spec, it shouldn't even have an O2 sensor to begin w/, and to check the brain under the driver's seat and see if there's some weird black box wired to it. Sure enough, there it was, labeled "Prototype I". It was basically feeding the O2 sensor info into the Euro-spec brain, which helped the car pass emissions inspection, but caused it run like crap.

Well, good news for me, you don't need emissions after 25 years in VA - so this was the last year I needed it. So, I disconnected the black box from the brain, unplugged the O2 sensor, and put in the chip - and the car runs like an absolute dream, literally night and day difference. No idle trouble, even on cold starts, tons of power on low revs, and throttle response is exponentially better.

Not sure if this addresses your specific issue - but thought I would share w/ folks just in case anyone else is struggling w/ something similar.

Rick K

Oh yeah - M&K exhaust going on early next week.

911_pilot

Thanks for the input guys.

The new 02 sensor should be of no affect during the warm up phase for the first few (to several seconds). It only comes online when it reaches full operating temperature (electrically), which then shuts off (electrically)when the exhaust gases heat the probe tip as it reaches full temp and begins to send an electrical signal to the DME on it's own. At the initial idle at start, the 3.2 is running on a set of parameters set by the CHT, WAR, Throttle position, speed sendors, and Altitude sensor if needed. (DME map parameters)

The issue is the "additional" inputs such as vacuum leaks, bad sensors, shorted wires, electrical grounds,....the funs stuff to chase down.

The CHT is beginning to attract more attention in my book. Although the ohms are reading in the correct range, it could be an issue. As mentioned I need to get to a good wrench with an engine gas analyzer to get the CO in correct range. A couple of posts suggest that made all the difference.

I was hoping to hear that the Warm Air Regulator was giving the group issues.
On race engines these devices go away completely, and the ports are blocked off. On stock engines I read many problems here on Rennlist and the Pelican Boards.

I appreciate the moral support!! I am sure that I will laugh at myself when the fix is found. This has to be simple....


I will start at page 1 and go back through the steps to assure that I have not missed something before "part swapping" begins.

any further guidance will be very appreciated....

911_pilot

J. Brinkley

when you say Warm Air Regulator, are you talking about the thing by the oil filler neck?

Rick K

By the way, here's the pic of that "black box" I mentioned...

911_pilot

J. Brinkley,
Yes, the Warm Air Regulator is the "thingy" by the filler neck.
It is basically an air valve that allows warm air from the oil tank into the intake at certain air temperatures.

J. Brinkley

just checking because if you want to rule that out you can put a small clamp on the short jumper hose that goes from the thermo switch to a port just under the butterfly on the TB.
the thermo switch is a plug on the back, its the thing with the blue plastic on it.
one hose from the WAR to the thermo switch and the short one from the thermo switch to the intake under the butterfly, clamp that one to rule out the WAR.
I wouldn't think thats the problem though.

thats an old pic, excuse all the extra stuff on there

scottb

Have you tried something as simple as having the mixture checked and adjusted?

911_pilot

Jerry,
I did check this little plug. Perhaps the best single increase in in performance was finding that the PO (or his wrench) had allowed the vacuum hose from the "switch" on the throttle body to the WAR to become disconnected. It had swelled from age. I cut about .75" inches off to new fresh section and reinstalled.
BOOM! Major vacuum leak resolved. This particular leak caused the engine to pop and stall at idle as if it had a very tall cam. (Like a ford 289 with a .380/.380 cam)
ScottB is suggesting a exhaust gas check. Other than the emission check downstream of the catylatic converter (showed 0.0 CO) I have not. This is on my schedule after eliminating all of the "physical" or "mechanical" issues. Valve adjustment, vacuum leaks, properly operating sensors, etc. I was thinking like ScottB. That I had it down to a simple adjustment....and then it got cold here.
The single item that is throwing me is that the engine ran perfectly when it was below fifty degrees. It ran fine until it warmed up a bit. If it were a mixture issue, I am not sure that the "cold" would make a difference. Does this make sense?
If temperature was a factor that made the mixture better....(guessing here) then it would almost positively be the cylinder head temp sensor (which checks fine on the ohm meter) or the warm air regulator (which I don't know how to test..yet). I will get a gas analyzer on and have the engine set properly. All suggestions are greatly appreciated. That's how we learn.

J. Brinkley

I think you're fine, once you do all the top fixes let someone set the idle mix and I bet it will be fine.
A friend of mine had a bad cht that let the car start and drive when cold, but would sputter and die once it was warm.
they're not expensive, but a pain in the butt to change. If it's an old one maybe you want to replace it.

scottb

Actually, differences in outside air temp change the volume of oxygen per cubic foot of air. If your mixture was just on the edge, a change in air temperature could cause your car to run poorly. And, besides, a mixture check and adjustment could be an easy fix compared to replacing parts.

Good luck.

Keep us posted.

Robert Buchanan

ScottB,
While I agree that air temperature does change the density of the molecules of outside air in a given space...the difference at 43 feet above sea level is small. On my particular '86, an altitude sensor is installed as compensator. (That is another unknown currently. It is possible that the Altitude Dashpot has cracked inside and is telling my engine that I am at 15K feet.
I may remove the WAR this weekend and take a look. It may be gummed up as it takes air directly out of the oil tank when operating.
The CHT is still knawing at me a bit. I have read hundreds of posts suggesting that this was an issue.
The air mixture is a simple fix and I am trying to get in on Friday for evaluation before removing and cleaning anymore. At the last concours, my engine scored 76 out of 80 if that tells you anything. :-)
Thanks again for the support.