[astroede]

I know, I know, the idle speed variation in the attached video is not much. And I'm not saying that anything is wrong. But since I haven't been in any other 968's, I don't know what is normal. My idle "wanders" a bit, going slightly up and down, and I'm just wondering if this is typical for a 968. Sorry if I am being anal, but thought I should ask the experts before I start poking around in the engine compartment unnecessarily. A video of my tach while idling: http://www.youtube.com/watch?v=mwOGJzAvLR8

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[flash]

fairly normal - a certain amount of fluctuation is to be expected - that may be on the edge though - the cap and rotor are usually the culprit - they only last about 10k miles before they start doing stuff like that - take a look - if there is wear or pitting on the contacts, change them



also, when is the last time you cleaned the MAF with MAF Cleaner?

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[astroede]

Thanks, Flash, I was counting on hearing from you. I bought the car in June 2010, and I have no record of the MAF ever being cleaned, so sounds like I should start there and see if that improves it? Cap and rotor were replaced 11K miles ago (2005).

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[Cloud9...68]

My car's idle behavior is similar to yours. I've replaced the distributor cap and rotor, and cleaned the MAF, and it didn't impact my idle. Some people have removed and cleaned their idle stabilization valves (if you're interested, do a search; a former owner named JohannvB did a nice write-up on how to do it). It appears the valve is a bit of a pain to get to, but it looks like with a little patience, it probably isn't too bad of a job. Plus, the best part is that it's free. If you do it, let us know if it makes a difference.

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[flash]

these things are lumpy, and any number of things can affect idle - dirty injectors can do it - this is winter and we have oxygenated fuel - that can do it



i would do things in this order:







start by inspecting the cap and rotor - change if any signs of wear



clean the MAF with MAF cleaner only - do not turn on the key or start engine until fully dry



run some techron or run-rite through the fuel system

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[SILVY968]

I have had the idle moving issue for some time. New cap and rotor did not change it, nor did cleaning the idle stabilization valve or the MAF cleaning.

The best results come from techron injector cleaner; but the "hunting" soon reappeared, leading me to consider sending the injectors out for professional cleaning. Might get it done in April when I am due for a timing belt replacement.

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[flash]

common issue - it takes very little to upset an injector



unfortunately, i've had all of the above issues affect my idle, so a point by point will be required to isolate the problem - that's why i suggested the order i did - start with the cheap and easy, and move your way down the list - dirty injectors will require a couple of days of down time while they get done

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[Scott Collins]

Good thread - common problem.



Makes me wish that someone had shot video of a 968 in say, 1992, of a car with a about 1,200 miles on the odometer. Like to see what the tach (and other things) did then....



Scott

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[astroede]

Thanks for all the advice everyone. I'll work through the list of possibilities, and then post the ultimate fix (including another exciting video of my tach!) when I get it resolved. Could be a while, though...it's colder than you know what and my garage is not heated!

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[astroede]

First update: I bought a nice 23000 BTU kerosene convection heater at Lowe's, and it warmed the garage up nicely, so I got busy. Since it was clear that the idle control valve had never been removed and I wanted to get my hands dirty, I started there. It wasn't too difficult to remove the valve, following the excellent instructions posted on this site. The valve has a cylindrical "shutter" inside that was fairly blackened and probably gunked up (there is very little clearance so it wouldn't take much gunk to interfere with the proper motion; see blurry photo). A few squirts of carb cleaner and a couple Q-tips and the valve was clean and free moving. Reassembled and started the car. Immediate difference: the car idled higher (cold) and idled much smoother than on previous cold starts. Went for a drive...all was well...but...the idle variation was still there when the engine warmed up; not much difference. So...next step: cap and rotor inspection per Flash's suggestion. Stand by, more updates to follow.

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[apex]

astro - looking forward to hearing the results of your troubleshooting. ha - wanna know what fixed a worse idle speed delta than yours? a complete top-end rebuild did the trick :-) just about the only two things I did *not* do was clean the inside of the idle control valve or clean the injectors. but after the engine was all back together my idle speed was rock-solid. go figure.

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[flash]

yeah - there are so many things that can make the idle move around a bit, that sometimes it's hard to nail down - i was surprised when i saw how little scoring on the distributor cap and rotor that it took to make mine move nearly 100 rpm in an odd random fashion - i have been continually surprised at how quickly these parts show wear - i have yet to get more than 10k miles out of them before i can tell there is a difference, and i need to change them - yes, the engine still runs, and probably as well as most of the cars out there, and would probably continue to do so for a long time, but when i change them, i can tell the improvement



injectors will do it too, especially if you run less than stellar gas, or have a lot of miles on them since they were serviced - the running service interval is about 60k miles - most cars out there have not had them done within that period, and could benefit from such a service



an imbalance in compression will do it too - more than a 5lb variance from one cylinder to the next can easily cause this, as can having compression numbers too low (180 is about it)



but, as i said before, start with the easy and the inexpensive - you certainly won't hurt anything, and can only benefit by doing those things

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[astroede]

Apex - Glad to hear you got your idle speed variation problem solved. I will probably stop trying before I go that far since my variation is not so bad.



Update: Today I removed and inspected the distributor cap/rotor as Flash had recommended. This was very easy to do overall, except for one stubborn captive screw. As can be seen in the photos below, there was some pitting on the brass electrodes on both the cap and the rotor. Not sure how significant this amount of wear is relative to my idle issue; so I went ahead and ordered a new Bosch cap and rotor, and Karlyn-STI ignition wires, from Pelican for $218.25 including a $20 off certificate and free shipping. I will update this post once I have the parts installed and she's running again, in about a week.

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[flash]

the cap is toast, and looks like it has been for a while now



hard to tell from that shot on the rotor

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[astroede]

Tonight I installed a new distributor cap, rotor, and ignition wires. Video of the idle result below(sorry about the annoying door chime; I have the passenger door torn apart and couldn't close it). My opinion: basically same idle variation.



Next: MAF cleaner.



Things I learned while replacing the cap, rotor and wires: The cap bolts don't always come out easy, use some care so you don't strip the threads; the ignition wire "weave" is a little challenging in spots (I took pictures prior to taking it apart and assembled it one wire at a time on the work bench); and be very mindful of the three spacers on the back of the rotor so they don't fall off and drop into bad places.



I'll update this thread after the MAF cleaner.



http://www.youtube.com/watch?v=0cYt8VM41LM

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[TonD]

I have very similar idle speed variation on mine, meaning in the same rev-range, though mine does it a bit slower. Staying a tad longer stable and then short drop etc. I will follow this topic with much interest ;-)

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[flash]

i'm not sure that's all that abnormal



something that just dawned on me, and i apologize for not noticing this earlier, is that in both videos the oil pressure was pretty high at idle, indicating to me that the engine was cold - the idle will vary when cold, as the sensors are metering changing temps, and then adjusting things accordingly - there are a number of maps in the ECU for the idle, and temp is something that alters which one is used



that being said





depending on the mileage on the car, the condition of the valves and cylinders, and what the injectors are like, it could still be "normal" - does it seem like it's stumbling or anything? is there any hesitation?



high mileage engines (anything over 75k) will have a certain amount of carbon and compression variance that will cause any engine with a fueling system like ours to fluctuate a bit when the rpms are low



similarly dirty injectors will as well, as the fuel flow is not metered as smoothly as if they were clean



but as the variation is only about 75rpm, unless it seems like it's missing or something, or causing hesitation or stumbling, i am not sure i would go very far tracking it down



obviously a compression check is in order to make sure you had even compression, and all over 180



injector cleaning and balancing should be done at least every few years

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[Cloud9...68]

Yes, I had noticed the high oil pressure reading as well. I also agree that the degree of idle speed variation you're seeing doesn't seem bad at all - if that's your biggest problem, that's one fine 968 you have there!

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[SILVY968]

Is there an equal, yet less costly way to clean the injectors, other than to have then removed and taken to a specialist?

Brian

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[astroede]

Flash: There's no stumbling or hesitation. She runs great. It is possible that the engine was still a bit cold, but I have noticed the idle variation even in the summer at full temp. Haven't done compression check yet. The injectors haven't been cleaned to my knowledge, so there is a reasonable chance that the injectors are a contributor if not the cause. We'll see what effect the MAF cleaner has tomorrow. I am definitely not opposed to removing the injectors and having them cleaned and balanced (I relish any chance to get my hands on some wrenches). Anybody know if there is someone close to Chicago that can do the cleaning and balancing, or should I send them somewhere else?



Cloud9...68: This car has no problems that I am aware of (knock on wood) so I would say that she IS a very fine 968! The mechanic I took her to looked at the service records and told me that the previous service departments had gone a bit overboard on the maintenance frequency and timing, perhaps sensing that the previous owner had deep pockets. I'll post a spreadsheet of all the known significant maintenance if anybody would like to see a list from Day 1 (with labor and part costs too).



Silvy968: I have read that Chevron Techron is a superior injector cleaner preferred by many on this forum. I plan to try that as soon as I can actually put some miles on the car (we are still digging out from 2 feet of snow and subzero temps). Looks like a fairly easy job.

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