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Car Forum / Volkswagen / Water Cooled Volkswagen Cars / September 2008what would cause this idle behavior - 84 GTI
I have an 84 GTI, ~230k miles. Car starts great, idles around 900 rpm for about 30 sec, then idle drops off to about 600-700, so it almost stalls (and occasionally does). Over the next 15 minutes, the idle will slowly creep back up to 800-850, where it remains. She has new plugs, wires, rotor, dist. cap, o2 sensor, and a few new vacuum lines. I've checked vacuum lines for leaks, found none. Anything obvious to check first? Bentley notes a number of things (thermo-time switch, cold start valve, aux. air valve, CPR for instance), but not in any particular order for this kind of problem. I'm hoping someone has seen this symptom before and can say what causes it. Thanks. There is a valve on the right side strut tower that boosts the idle. I think there is one for AC and one for general purposes idle bumpup. You need to set the idle speed when warm with both of those power plugs unplugged. That idle speed slowly comes up as the system control pressure adjusts. It takes a bit of time for the Control Pressure Regulator to warm up with electrical heat and oil warm up. Check for vacuum leaks with unlit propane torch or carb cleaner. >I have an 84 GTI, ~230k miles. Car starts great, idles around 900 rpm >for about 30 sec, then idle drops off to about 600-700, so it almost [quoted text clipped - 6 lines] >in any particular order for this kind of problem. I'm hoping someone >has seen this symptom before and can say what causes it. Thanks. On Sep 22, 9:07 am, Jim Behning <jimbehn...@doesthisblockpork.mindspring.com> wrote: > There is a valve on the right side strut tower that boosts the idle. I > think there is one for AC and one for general purposes idle bumpup. [quoted text clipped - 17 lines] > > - Show quoted text - Are you talking about the "thing" next to the cold-start valve, that has a couple vacuum hoses coming into the bottom of it and a couple of 2-wire terminals at the top? This car has (non-functioning) A/C, btw. What is that valve called - I have not seen it described in Bentley, and never knew what it did. How does it work? And by adjusting the idle, I assume you just mean by turning the screw in back of the throttle body, right? Thanks for the quick response Jim, this sounds easy to try. Are you talking about the "thing" next to the cold-start valve Dunno about a GTI, but on my '81 Scirocco the thing below the cold-start valve is the auxiliary air regulator, and when it went bad the engine would not idle at all when cold (or even after sitting for a short time). > Are you talking about the "thing" next to the cold-start valve > > Dunno about a GTI, but on my '81 Scirocco the thing below the cold-start > valve is the auxiliary air regulator, and when it went bad the engine would > not idle at all when cold (or even after sitting for a short time). The Early model Sciroccos didn't come w/ the two units mention above, they were likely on the later MkII style Rocs though. Lot of under hood stuff was changed in '82 and in '84 for that matter. TBerk > > <meseal@gmail.com> wrote in message news:2730dd33-225f-4d07-af87-5c3d5ca82ed6@d45g2000hsc.googlegroups.com... > > Are you talking about the "thing" next to the cold-start valve > > [quoted text clipped - 5 lines] > they were likely on the later MkII style Rocs though. Lot of under hood > stuff was changed in '82 and in '84 for that matter. All MkI with CIS have a cold start valve and aux air regulator [valve]. There's also an EGR valve in the same general area on engines without a catalytic converter. >>> <meseal@gmail.com> wrote in message >>> [quoted text clipped - 13 lines] > There's also an EGR valve in the same general area on engines without a > catalytic converter. But we're not talking about those but the idle stabilizer mounted on the shock tower. Right? TBerk they did that when new off the truck!!! NO kidding! Try adjusting the CO% slightly richer. >I have an 84 GTI, ~230k miles. Car starts great, idles around 900 rpm > for about 30 sec, then idle drops off to about 600-700, so it almost [quoted text clipped - 6 lines] > in any particular order for this kind of problem. I'm hoping someone > has seen this symptom before and can say what causes it. Thanks. Also the Aux Air Valve can be adjusted by loosening the little nut and sliding it one way or the other and retightening it. Try idling the engine at 1K when it is warm and see how the idle is during its next warm up. Do you have good power during warm up? Check those fuel injector seals for vacuum leaks.  Signaturelater, (One out of many daves) >I have an 84 GTI, ~230k miles. Car starts great, idles around 900 rpm > for about 30 sec, then idle drops off to about 600-700, so it almost [quoted text clipped - 6 lines] > in any particular order for this kind of problem. I'm hoping someone > has seen this symptom before and can say what causes it. Thanks. On Sep 22, 9:37 pm, "dave AKA vwdoc1" <vwdoc1nos...@pleasehotmail.com> wrote: > Also the Aux Air Valve can be adjusted by loosening the little nut and > sliding it one way or the other and retightening it. [quoted text clipped - 23 lines] > > - Show quoted text - So I tried Jim's suggestion, and tweaked the idle screw a little. Idle is more stable now, but I don't know how disconnecting the idle air bypass valve (finally found that in the Bentley) would have made a difference. Checked for vacuum leaks with a propane torch, including the injector seals, and got no reaction from that. As to Woodchuck's comment, THIS car didn't do that new off the truck. I've had it for 22 years and this a new phenomenon for me. I will also try to see what happens if I adjust the aux air valve as Dave suggests. Power and response is good once I put my foot on the gas, even when cold. Could it be a sticking throttle plate, that gets less sticky as the engine warms up? Thanks for all your suggestions... One person spent $1200 to get a Scirocco saved from the junkyard to start and idle perfectly at anytime! OUCH! Almost everything was needed/addressed even the residual pressure device (fuel accumulator) located by the fuel pump. So do you want perfection, or are you willing to compromise with a couple of quirks with a 24+ year old car? I prefer spraying carb cleaner at those injector seals, but I don't use propane anyway! One day I might! ;-) When setting the warm idle BTB ()By The Book), you might have to disconnect and/or plug components. Some VWs you have to create a small vacuum leak by inserting/flipping a fitting. 8^o Signaturelater, (One out of many daves) On Sep 22, 9:37 pm, "dave AKA vwdoc1" <vwdoc1nos...@pleasehotmail.com> wrote: > Also the Aux Air Valve can be adjusted by loosening the little nut and > sliding it one way or the other and retightening it. [quoted text clipped - 24 lines] > > - Show quoted text - So I tried Jim's suggestion, and tweaked the idle screw a little. Idle is more stable now, but I don't know how disconnecting the idle air bypass valve (finally found that in the Bentley) would have made a difference. Checked for vacuum leaks with a propane torch, including the injector seals, and got no reaction from that. As to Woodchuck's comment, THIS car didn't do that new off the truck. I've had it for 22 years and this a new phenomenon for me. I will also try to see what happens if I adjust the aux air valve as Dave suggests. Power and response is good once I put my foot on the gas, even when cold. Could it be a sticking throttle plate, that gets less sticky as the engine warms up? Thanks for all your suggestions... >On Sep 22, 9:37 pm, "dave AKA vwdoc1" <vwdoc1nos...@pleasehotmail.com> >wrote: [quoted text clipped - 39 lines] >less sticky as the engine warms up? >Thanks for all your suggestions... If you know that vintage car well you will on occasion hear a click when the idle dips. That is that booster (intake air bypass valve) on the strut tower opening up and letting more air in. That also lets in more fuel bumping up the idle. If you hear your car clicking a lot then you know you need to properly adjust the idle speed. No I was not talking about the warm up air regulator mounted on the intake. See pages 58-59 of your Bentley Rabbit 1980-1984 gas service manual in the fuel section. The manual does their procedure different from what I did. I unplug the connectors on the idle air bypass valve so it is not trying to boost the idle speed. I adjust my idle speed and then reconnect the electrical connector. They speak of clamping down on the air hose so it is not supplying "false" air. I have never played with the settings on the auxiliary air regulator but I have often looked at it wanting to but I resisted. Well if it is running better then you may be done. I did have plenty of crud in all my fuel screens. I bought my 84 from a junkyard with no hood, gas cap or seats. I replaced a few injection things due to clogging over those yeras of ownership. Having a vehicle most its whole life is much easier to maintain as there hopefully is less jerry rigging to undo. "Jim Behning" wrote in message snip > I have never played with the settings on the auxiliary air regulator > but I have often looked at it wanting to but I resisted. Only if you need/want to! ;-) > Well if it is running better then you may be done. I did have plenty > of crud in all my fuel screens. I bought my 84 from a junkyard with no > hood, gas cap or seats. I replaced a few injection things due to > clogging over those yeras of ownership. Having a vehicle most its > whole life is much easier to maintain as there hopefully is less jerry > rigging to undo. I seem to remember that some inlet bolts for the fuel distributor could have a screen on them too. >"Jim Behning" wrote in message > [quoted text clipped - 14 lines] >I seem to remember that some inlet bolts for the fuel distributor could have >a screen on them too. Yes they do if no one has removed the screens. I ampretty sure the lines to the injectors or the ports of the fuel distributor had them also. On Sep 23, 11:32 pm, Jim Behning <jimbehn...@doesthisblockpork.mindspring.com> wrote: > On Tue, 23 Sep 2008 16:59:47 -0500, "dave AKA vwdoc1" > [quoted text clipped - 24 lines] > > - Show quoted text - So it sounds like I might want to check fuel-flow related items too, like these little screens. I know for a fact that the only thing that has ever been done on the fuel system on this car in its whole life is replacing the fuel filter every couple of years, and the fuel pump relay just last month. Everything else is as it was when it left the factory, from tank to injectors and everything in between. I don't ever remember hearing a 'click' from the air bypass valve, but I never really listened for it. I will follow the checks described in Bentley to see if it is actually functioning. Bentley doesnt describe how to repair it though; I wonder if these are available as replacement parts online? I don't mind a few quirks and compromises - I'm already living with plenty of those (window regulator, head liner, balky temp guage, bad radio reception, a wife and 4 kids....) But I am trying to keep up with the driveability things, plus I'm enjoying learning how all this works after all these years. Thanks for your help and ideas. >On Sep 23, 11:32 pm, Jim Behning ><jimbehn...@doesthisblockpork.mindspring.com> wrote: [quoted text clipped - 44 lines] >with the driveability things, plus I'm enjoying learning how all this >works after all these years. Thanks for your help and ideas. Those screens take just a few minutes to clean. Of course you want to not spill and crud/rust into anything. My car had issues because of a missing hood and a gas cap. There is a chance your screens are ok since you owned it since nearly new and kept up on basic maintenance. I just had this same thing and it turned out to be my fuel pressure regulator was bad. it was letting fuel into the intake and failing my low idle CO % 35 bucks at pep boys vs 169 at foreign after market I would never imagine Pep Boys would have a cpr. It is an antique car, it is a low volume part for them... >I just had this same thing and it turned out to be my fuel pressure >regulator was bad. >it was letting fuel into the intake and failing my low idle CO % 35 >bucks at pep boys vs 169 at foreign after market Doesn't even sound right since the CPR on a 1984 would not let fuel into the intake directly! Maybe the fuel pressure regulator on a 1988+ Digifant fuel injection system. >I would never imagine Pep Boys would have a cpr. It is an antique car, > it is a low volume part for them... [quoted text clipped - 3 lines] >>it was letting fuel into the intake and failing my low idle CO % 35 >>bucks at pep boys vs 169 at foreign after market On Sep 28, 10:11 am, "dave AKA vwdoc1" <vwdoc1nos...@pleasehotmail.com> wrote: > Doesn't even sound right since the CPR on a 1984 would not let fuel into the > intake directly! [quoted text clipped - 9 lines] > > - Show quoted text - Update on situation from the original post: Last week, the problem got a lot worse. After idling better for a couple days, she stopped idling at all. If I lifted my foot off the gas, engine warm, she just sputtered down and died. So I had to feather the gas pedal constantly while working brake and clutch with the left foot. I drove like that for 2 days - it's very hard to work 3 pedals simultaneously with only 2 legs. This weekend I did the following: - tested the cold start valve per Bentley; sprays fine, no leaks. - removed and cleaned and lubed the throttle body. Pretty cruddy on the inside. - removed and cleaned the sensor plate (?) in the air flow meter. It too was cruddy on the bottom. Also noticed that it was sitting a couple mm's lower than the info in Bentley indicated it should. I bent the little spring below the lever to raise it up, so now the top of the plate is even with the top of the narrowest part of the venturi. I don't think this changes the mixture. - replaced 4 vacuum hose connectors; they seemed ok, but a little dry- rotted on the outside cloth covering. - installed an o-ring on the idle screw shaft. There is some sort of plastic sealing ring on it, but the screw felt too loose and turned too easily, so this tightened it up and sealed it good. Car idled smooth at 1100 rpm this morning; I'll need to crank the idle screw back down I think. Keeping my fingers crossed..... Don't know what of the above actions had the most effect. I suspect adjusting the sensor plate had the most impact. |
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