Strange Hot Idle Event
05-08-2010, 01:42 AM
#16
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I'll check vacuum this weekend.
As has already been said on here, the fact that the engine cuts off at 1400-1500 RPM indicates that the idle switch is closed and working, so it would not seem that sticking throttles, tight cables, etc. are the problem.
Sounds like false air (vacuum leak) or a sticking ISV are the two usual suspects. Those would seem to be the most likely source for air getting around a closed throttle plate.
Of course, if the idle switch is maladjusted, so that the throttle can be open with the switch still closed...
Sounds like false air (vacuum leak) or a sticking ISV are the two usual suspects. Those would seem to be the most likely source for air getting around a closed throttle plate.
Of course, if the idle switch is maladjusted, so that the throttle can be open with the switch still closed...
ISV is new, (old one was actually seized solid and the car idled just fine before I started the refresh....go figure) and bench tested prior to install. I'll be double checking the vacuum lines this weekend, but have already done a lot of work with these lately.
This just seemed to happen "out of the blue" that's why it kind of freaked me out. I've put a couple thou on the car since the top end job, and all seemed close to good. I say close because the idle never seemed quite right to me. a little high. (IMHO). But not a lot, and within spec. I have screwed around with the cables quite a bit though. I'm almost thinking it's something there, but....
05-08-2010, 01:47 AM
#17
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Been There
I've already cleaned and checked a number of the ground points. All's good there.
I may go back with the ohmeter if I can't find another solution though.
Thanks!
05-08-2010, 01:50 AM
#18
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Thanks John.
John, Thanks for the input. it's really starting to look like a Vacuum Issue. I was pulling about 20 in Hg immediately after the refresh. I'll test again this weekend and report back.
05-08-2010, 01:51 AM
#19
Under the Lift
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05-08-2010, 10:01 AM
#20
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Drive the car. With the dash read-out set to instant mileage, coast down from 2000 (actual RPM not critical) to 1400 RPM with your foot completely off the throttle. You should see 90 mpg until you get well under 1500 RPM, at which point the mileage should drop below 90.
Repeat the process with the throttle just barely pressed - you should never see 90 mpg, as the idle switch should open as soon as the throttle is even touched.
If you can get 90 mpg with slight pressure on the throttle, then the throttle switch may be maladjusted.
Repeat the process with the throttle just barely pressed - you should never see 90 mpg, as the idle switch should open as soon as the throttle is even touched.
If you can get 90 mpg with slight pressure on the throttle, then the throttle switch may be maladjusted.
05-08-2010, 10:45 AM
#21
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928 At Last,
The problem with reading out a cable with an ohhmeter is that it won't show the cable's load-carrying capability, though it may read out perfect continuity. I verified this the other day when I was replacing my ground straps. Both read perfect, but the engine ground was shot.
The problem with reading out a cable with an ohhmeter is that it won't show the cable's load-carrying capability, though it may read out perfect continuity. I verified this the other day when I was replacing my ground straps. Both read perfect, but the engine ground was shot.
05-09-2010, 10:03 PM
#22
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OK, first results
Got an audio on the idle position TPS. Sounds like it's working. I'll check the digital response tomorrow on the commute to the office.
Thanks for the input!
05-10-2010, 12:04 AM
#24
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05-10-2010, 11:39 AM
#25
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Hmmm, hope this isn't a hijack, but I've been wanting to figure out a similar issue on my car, and Wally's suggestions bring it to mind ...
Referring to post #20, my car does exactly what he describes on 'coast down' with closed throttle.Shows 90 MPG down to a certain point then reverts to another number, like 36.7 or something. What happens nex is odd though ...the engine will cycle back and forth ... drifting upward to about 1,400 rpm, then pulling back down to about 1,200. It's as though the electronics are battling some influence that makes the car gain RPM "on its' own".
I notice this mainly on downhill roads, not on level roads, so maybe the road speed is increasing and pushing the engine speed up in the process, starting the cycling effect?
I just did the entire top end job on my car, checked the TPS adjustment, replaced all vac lines, etc. and it idles rock-steady at 675 rpm in gear. This closed-throttle cycling effect has always been present and didn't change following all that work ...
Referring to post #20, my car does exactly what he describes on 'coast down' with closed throttle.Shows 90 MPG down to a certain point then reverts to another number, like 36.7 or something. What happens nex is odd though ...the engine will cycle back and forth ... drifting upward to about 1,400 rpm, then pulling back down to about 1,200. It's as though the electronics are battling some influence that makes the car gain RPM "on its' own".
I notice this mainly on downhill roads, not on level roads, so maybe the road speed is increasing and pushing the engine speed up in the process, starting the cycling effect?
I just did the entire top end job on my car, checked the TPS adjustment, replaced all vac lines, etc. and it idles rock-steady at 675 rpm in gear. This closed-throttle cycling effect has always been present and didn't change following all that work ...
