RPM Surge After WOT, Weird Idle, Worried I’ll damage my engine |
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RPM Surge After WOT, Weird Idle, Worried I’ll damage my engine |
drewvw |
Aug 23 2019, 07:40 PM
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#1
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new england car guy Group: Members Posts: 1,631 Joined: 24-February 06 From: Boston, MA Member No.: 5,630 Region Association: North East States |
Hi All, experiencing a tricky problem and I’m worried I’ll blow the engine if I don’t figure out.
73 1.7, fly cut heads, SSI/aftermarket exhaust, mostly stock otherwise. Core Symptoms: - Idle rpm inconsistent. Steady, but it seems to keep changing its mind on whether it’s 400, 1000, 1500. Decides again after you’ve been driving and slowing down for a stoplight or something. Gets a bit better when warm. - If I floor it, when I change gears the RPMs continue to zoom to redline levels. Can’t say for sure it’s an air leak type of surge, might be sensor or linkage (investigating next) based. Does not seem “floaty” like air if that makes sense, more hard. I’ve owned the car a long time and it general it runs great. But this has been an issue all summer. Just replaced exhaust and shored up SSI. Pretty Thorough review of vacuum lines, points, sensors, timing, etc. Swapped in another MPS. Looking for ideas here, tonight was scary with the RPM revs. Will update as a evaluate more. Thank you are any help! Drew |
Rand |
Aug 23 2019, 07:47 PM
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#2
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Cross Member Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None |
Sounds like a vacuum leak. Are we to assume it is still FI?
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drewvw |
Aug 23 2019, 07:56 PM
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#3
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new england car guy Group: Members Posts: 1,631 Joined: 24-February 06 From: Boston, MA Member No.: 5,630 Region Association: North East States |
Yup, stock D-jet. Have put in a good amount of time looking for leak spots, have not come up with anything thus far. Propane and eyeballs/wiggles. I’ll take suggestions on locations for sure!
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Rand |
Aug 23 2019, 07:58 PM
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#4
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Cross Member Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None |
What would fly cut heads and ssi exhaust have to do with any of this?
Idle hunting with djet is almost always a vacuum leak or lean condition. Have you checked valves and adjusted timing, and was that all good? If not, do it first. Gotta start with a foundation. |
theer |
Aug 23 2019, 07:59 PM
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#5
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Senior Member Group: Members Posts: 675 Joined: 31-July 15 From: Dover, MA Member No.: 19,014 Region Association: North East States |
Throttle cable sticking... return spring weak/broken?
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theer |
Aug 23 2019, 08:00 PM
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#6
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Senior Member Group: Members Posts: 675 Joined: 31-July 15 From: Dover, MA Member No.: 19,014 Region Association: North East States |
double post
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Rand |
Aug 23 2019, 08:02 PM
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#7
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Cross Member Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None |
No, sticking cables don't cause hunting, they cause sticking.
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drewvw |
Aug 23 2019, 08:04 PM
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#8
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new england car guy Group: Members Posts: 1,631 Joined: 24-February 06 From: Boston, MA Member No.: 5,630 Region Association: North East States |
What would fly cut heads and ssi exhaust have to do with any of this? Just brain dumping config to expose all potential variables and try to give you guys all info upfront (as a courtesy). Return spring looks okay but the whole linkage setup looks worn/old enough investigate and rule out. Timing and other foundational stuff done but will check again. |
76-914 |
Aug 24 2019, 08:46 AM
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#9
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Repeat Offender & Resident Subaru Antagonist Group: Members Posts: 13,455 Joined: 23-January 09 From: Temecula, CA Member No.: 9,964 Region Association: Southern California |
Sounds like the MPS is going south. (IMG:style_emoticons/default/beerchug.gif)
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dr914@autoatlanta.com |
Aug 24 2019, 08:58 AM
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#10
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914 Guru Group: Members Posts: 7,772 Joined: 3-January 07 From: atlanta georgia Member No.: 7,418 Region Association: None |
I would agree to first check for a sticking throttle cable. THEN
Check the vacuum retard/ advance, and the advance weights check the decel valve check the aux air valve check in general for vacuum leaks, most probably a split in a vacuum elbow, or a hose directly connected to the intake manifold Throttle cable sticking... return spring weak/broken? |
Rand |
Aug 24 2019, 09:00 AM
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#11
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Cross Member Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None |
Hey Geo, how does a cable cause hunting idle? Sticking for sure, but hunting is not mechanical which would stick. Guess what, we wasted that minute and are back to vacuum. And bonus points for LEAN.
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rjames |
Aug 24 2019, 06:51 PM
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#12
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I'm made of metal Group: Members Posts: 3,876 Joined: 24-July 05 From: Shoreline, WA Member No.: 4,467 Region Association: Pacific Northwest |
Hey Geo, how does a cable cause hunting idle? Sticking for sure, but hunting is not mechanical which would stick. Guess what, we wasted that minute and are back to vacuum. And bonus points for LEAN. He said the idle was steady, not hunting, but that it idles at varrying rpms. That could be a weak throttle body return spring or sticking throttle cable, among other things. When it idles high, can you bring down the rpms by manually pulling on the throttle cable in the engine bay to ensure the butterfly is closed? Also, what is meant by ‘if I floor it when I change gears the rpms continue to zoom to redline levels’? I would expect the rpms to go up when you floor it. |
Rand |
Aug 24 2019, 10:58 PM
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#13
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Cross Member Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None |
Hey Geo, how does a cable cause hunting idle? Sticking for sure, but hunting is not mechanical which would stick. Guess what, we wasted that minute and are back to vacuum. And bonus points for LEAN. He said the idle was steady, not hunting, but that it idles at varrying rpms. That could be a weak throttle body return spring or sticking throttle cable, among other things. When it idles high, can you bring down the rpms by manually pulling on the throttle cable in the engine bay to ensure the butterfly is closed? Also, what is meant by ‘if I floor it when I change gears the rpms continue to zoom to redline levels’? I would expect the rpms to go up when you floor it. Good catch Robert. I was thinking hunting. Dang he edited! LOL If it doesn't hunt then is is likely mechanical. |
drewvw |
Aug 25 2019, 07:59 AM
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#14
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new england car guy Group: Members Posts: 1,631 Joined: 24-February 06 From: Boston, MA Member No.: 5,630 Region Association: North East States |
Thanks guys this is helpful. Looking to get back into it today. I meant when I accelerate hard and release gas to shift it was like I still had the pedal down. And yeah the way the idle changes it does seem like it could be cause the throttle plate not closing all the way. I’ll report back. Very much appreciated! |
rhodyguy |
Aug 25 2019, 10:08 AM
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#15
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Chimp Sanctuary NW. Check it out. Group: Members Posts: 22,042 Joined: 2-March 03 From: Orion's Bell. The BELL! Member No.: 378 Region Association: Galt's Gulch |
If you disconnect the throttle cable at the throttle body, does the cable move freely without any binding?
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drewvw |
Aug 29 2019, 12:31 PM
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#16
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new england car guy Group: Members Posts: 1,631 Joined: 24-February 06 From: Boston, MA Member No.: 5,630 Region Association: North East States |
I've done another round of investigation, here is what I've found. In summary, it appears to be a combination of both the cable issue and an air related leak:
- Went through cable from pedal to throttle body. After doing so, cannot reproduce the "redline RPM with pedal released" condition. So that's good. - Timing is fine. New points and condenser. - I am still experiencing an issue with having two idle different idle speeds. Link to a video showing the issue is below. Car will have a very low (400 rpm) idle. If I drive the car OR sit in neutral and hold the car steady at 3500 RPM, when you release the pedal the idle will settle at 2100 rpm. If I put the car in gear and drive at low RPMs usually the idle will reset back to the 400pm level. https://www.dropbox.com/s/1dahe0hdhb3hr1d/IMG_1002.MOV?dl=0 - If the idle is at the 2100 pm level and I yank/wiggle the thottle cable, no effect. - Went through all the air hoses again and checked for leaks. Used propane and starting fluid plus visual check. AAR is working fine. Next step is to try and bypass the decel valve. So getting closer and the car is drivable again but something is clearly wrong and elusive. Thanks again for all input! |
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