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#1
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New bug, fast idle.
My 1992 Miata has started idling around 1800 rpm several days ago. It began happening very intermittently but it's almost all the time now. Miata.net isn't very helpful but I may not be looking in the right place? Today it stayed high all the time I was running errands* and it doesn't matter if the AC is on or off but... FWIW, I left the engine running and opened the hood to check the dashpot when I got home, it was OK but when I wiggled the cable the idle dropped down to normal but.. the cable was and always has been slack, maybe even a little too much slack according to the manual so it's not the cable hanging up.... also, manually trying to move the cable pulley has had no effect so I'm sort of thinking it's something in the ECU telling it to idle fast? I'd really appreciate it if someone will tell me it's either a simple adjustment or a $1.98 part.... but I don't think so. <sigh> *Running errand in 109F sunshine! I think just 5 more degrees and I'm gonna put the top up and turn on the AC. |
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#2
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New bug, fast idle.
XS11E wrote:
>My 1992 Miata has started idling around 1800 rpm several days ago. It >began happening very intermittently but it's almost all the time now. > >Miata.net isn't very helpful but I may not be looking in the right >place? > >Today it stayed high all the time I was running errands* and it doesn't >matter if the AC is on or off but... FWIW, I left the engine running >and opened the hood to check the dashpot when I got home, it was OK but >when I wiggled the cable the idle dropped down to normal but.. the >cable was and always has been slack, maybe even a little too much slack >according to the manual so it's not the cable hanging up.... also, >manually trying to move the cable pulley has had no effect so I'm sort >of thinking it's something in the ECU telling it to idle fast? > >I'd really appreciate it if someone will tell me it's either a simple >adjustment or a $1.98 part.... but I don't think so. <sigh> > > >*Running errand in 109F sunshine! I think just 5 more degrees and I'm >gonna put the top up and turn on the AC. > > > For what it's worth: Similar symptoms in my '92; turned out to be a faulty/shot "thermistor." (The thing is located near the firewall, I think on the block.) It sensed the engine water temperature to be cold, when in fact it was normal running temp. The ECU, thinking "cold engine," upped the idle to 1800 rpm, just as yours. Although I don't remember, the part was quite a bit more than $1.98. Let us know what you find out. '92 B; red, of course |
#3
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New bug, fast idle.
Stuff > wrote in
: > XS11E wrote: > >>My 1992 Miata has started idling around 1800 rpm several days ago. >> It began happening very intermittently but it's almost all the >>time now. > For what it's worth: > > Similar symptoms in my '92; turned out to be a faulty/shot > "thermistor." (The thing is located near the firewall, I think on > the block.) It sensed the engine water temperature to be cold, > when in fact it was normal running temp. The ECU, thinking "cold > engine," upped the idle to 1800 rpm, just as yours. > > Although I don't remember, the part was quite a bit more than > $1.98. Darn, I was afraid of that! I don't think that would cause an intermittent failure though? > Let us know what you find out. I will, I'll probably have to take it in and sell a couple of the children to pay the bill.... |
#4
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New bug, fast idle.
XS11E wrote: > My 1992 Miata has started idling around 1800 rpm several days ago. It > began happening very intermittently but it's almost all the time now. > > Miata.net isn't very helpful but I may not be looking in the right > place? > > Today it stayed high all the time I was running errands* and it doesn't > matter if the AC is on or off but... FWIW, I left the engine running > and opened the hood to check the dashpot when I got home, it was OK but > when I wiggled the cable the idle dropped down to normal but.. the > cable was and always has been slack, maybe even a little too much slack > according to the manual so it's not the cable hanging up.... also, > manually trying to move the cable pulley has had no effect so I'm sort > of thinking it's something in the ECU telling it to idle fast? > > I'd really appreciate it if someone will tell me it's either a simple > adjustment or a $1.98 part.... but I don't think so. <sigh> > > > > > *Running errand in 109F sunshine! I think just 5 more degrees and I'm > gonna put the top up and turn on the AC. XS11E, I have a few suggestions...they may not be right, but they're free/very cheap to check. 1) Check to make sure the cable pulley is well lubricated along both the point-of-contact with the cable and where it connects to the throttle body. On the cable I'd recommend lithium grease, but others might say otherwise for the actual joint. 2) Remove the intake piping from the throttle body. Say hello to your butterfly valve. With your (clean) finger, poke at it (on the bottom half, I believe) and see how easily it moves. Keep an eye out for any obstructing debris in there. Lubricate where the butterfly valve joins to the throttle body. 3) This may be a case of a loose idle valve somewhere. Notice how when the car is cold, it idles at a different speed? There's usually two idling lines that allow specified amounts of air in. I'm not sure how this works on a Miata, but it's something to look into. 4) Gas pedal sticking? Also, some things to ponder: does it only happen when it's that absurdly hot out? Does the idle jump even higher when you turn on the AC/radio/12V microwave oven? Keep fiddling! -r0ll |
#5
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New bug, fast idle.
r0lliSl1fe wrote:
> I have a few suggestions...they may not be right, but they're free/very > cheap to check. Thanks, I appreciate them! > 1) Check to make sure the cable pulley is well lubricated along both > the point-of-contact with the cable and where it connects to the > throttle body. On the cable I'd recommend lithium grease, but others > might say otherwise for the actual joint. I'll check that. Hadn't thought of doing that. > 2) Remove the intake piping from the throttle body. Say hello to your > butterfly valve. With your (clean) finger, poke at it (on the bottom > half, I believe) and see how easily it moves. Keep an eye out for any > obstructing debris in there. Lubricate where the butterfly valve joins > to the throttle body. I don't think it could be anything in there causing the butterfly to stick because I've tried closing it from the outside and it seems to be closed tightly but I'll take a look and see what I can find from the inside. > 4) Gas pedal sticking? No, the cable is slack when the car is idling fast so I've eliminated that, along with the cruise control cable, etc. The problem has to be right at the throttle body but from checking so far I'm pretty sure it's the ECU telling it to idle fast, not the butterfly failing to close. > Also, some things to ponder: does it only happen when it's that > absurdly hot out? I don't know, we've only got a cool nice comfortable 110F and won't get down to the too-cold-to-support-human-life temperatures of 85F and below for several more months... > Does the idle jump even higher when you turn on the > AC/radio/12V microwave oven? Here's something a bit weird. Before the problem, when I'd turn on the AC the idle would start to drop and almost immediately go back to a normal 1,000 rpm. Now, when it's idling up at 1,800 turning on the AC acts the same, the idle speed just barely starts drop and then immediately goes back to 1,800. It's as if the ECU is saying the correct idle speed is 1,800rpm and is keeping it at that speed AND that's why I don't suspect any mechanical problem but... I'll keep checking as that's all I can do. Oh, FWIW, I've not had a "check engine" light at all, whatever's happening the computer thinks is normal. |
#6
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New bug, fast idle.
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#7
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New bug, fast idle.
In article >,
XS11E > wrote: > OK, the fast idle problem is fixed. Anyone want to make a guess as to > the problem? The wire fell off the temperature sensor. -- Lanny Chambers '94C, St. Louis http://www.hummingbirds.net/alignment.html |
#8
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New bug, fast idle.
Lanny Chambers > wrote in
: > In article >, > XS11E > wrote: > >> OK, the fast idle problem is fixed. Anyone want to make a guess >> as to the problem? > > The wire fell off the temperature sensor. Not even close! |
#9
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New bug, fast idle.
In article >,
XS11E > wrote: > >> OK, the fast idle problem is fixed. Anyone want to make a guess > >> as to the problem? > > > > The wire fell off the temperature sensor. > > Not even close! Um...the tach was wrong, and it wasn't actually idling too fast? Crikey, how should we know? :-) -- Lanny Chambers '94C, St. Louis http://www.hummingbirds.net/alignment.html |
#10
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New bug, fast idle.
Lanny Chambers > wrote in
: > In article >, > XS11E > wrote: > >> >> OK, the fast idle problem is fixed. Anyone want to make a >> >> guess as to the problem? >> > >> > The wire fell off the temperature sensor. >> >> Not even close! > > Um...the tach was wrong, and it wasn't actually idling too fast? > > Crikey, how should we know? :-) I wish one of you had told me, apparently it's not a rare problem. I took it to Mike's Place: http://www.mikes-place.biz/ After talking to Mike on the phone, he just asked the year and then said it might be the IAC but most likely was the PVC valve and he could look at it at 2pm. The PVC valve had lost it's innards and was just an empty shell. The extra air caused the ECU to add fuel and the car ran just like I was stepping on the gas. Since the problem was entirely mechanical, no Check Engine Light. Mike had a PCV valve for $5.00 and I was off and running (with proper idle speed) about 20 minutes after I brought the car in.... As I've said hundreds of times before, it's hard to diagnose a problem as fast as someone who's seen it before! |
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