Jump to content

Idle speed gone nutty


Recommended Posts

I was coming back from an appointment this morning, and the idle speed on my coupe decided to Double (13 - 1400 rpm) for some reason. Could not make the speed go down with the brake/in gear and there are no codes?????

Any suggestions please????

Thanks,,

Nic

Link to post
Share on other sites

Hey Nic - I may be way off, yours may be a ECM deal. But check the mechanical throttle, it may be stuck a little.

I fired up the old wagon to sell it and Ill be danged if the throttle didnt stick

at pretty high RPM, I got under the hood and worked it loose, it had just been sitting for a year I guess.

Hope you figure it out.

Link to post
Share on other sites

Darn...what a response - Thanks everyone :). I went out after Reattatudes/Dave's response/suggestion, and could not see where anything was in a bind. Afterwards I drove the coupe to get a haircut, and it was still acting up. Also did several errands and home now (9:47 P.M.) - still acting up. I will

take Dave'89, Padgetts, and BrentS suggestions and apply tomorrow. Of note >>> I did the Seafoam procedure this last Saturday. I Let the Seafoam in slow, let it sit 15-20 minutes, started and it smoked for about 5 minutes at increased RPM >>> , but maybe my imagination - it seemed to run like a scared rabbit afterwards :). Just wondering if the Seafoam could possibly have anything to do with the current difficulties / problems????

Thanks again,,,

Nic

Edited by nic walker
spelling cold - could (see edit history)
Link to post
Share on other sites

Thanks for all the great replies. I have been tinkering with the coupe and all of the suggestions all afternoon. I came in for a mental health drink about 3:30. When I went back out around 4:30 and started it again it was idling correctly (story of my life :( ). I cleaned the IAC (not that dirty), lubed linkages, checked all vacuum lines including the one I took off to deliver the Seafoam (hose/line feels weak - dry rotted and needs replacing), and performed several other tasks. Another note I forgot to mention is that I did a full tranny fluid change per F14's procedure (included torque convertor fluid - changed all 14 quarts and replaced the filter when I did the SeaFoam Saturday). I have driven it about 10 miles in drive time traffic and it seems fine now. I am going to definitely replace some of the vacuum lines.

Sincere thanks for all of the suggestions - greatly appreciated-----just wish I could report a more definite resolution.

:)

Nic

Link to post
Share on other sites

Yes, good questions Ronnie...........my low coolant temp (160 F) caused my ECM to "command" the IAC to be open a little more than usual..............kinda like when you first start the engine when cold. My low coolant temp was related to the infamous crappy T-stat gasket design.

The tricky thing was, that after the idle came down (once engine warmed up), the high idle condition would re-appear 20 min later; kinda like as if the ECM was expecting the temps to have climed higher than 160F by that time, yet they never did.

I fixed T-stat gasket issue, and went back to stock 195F T-stat........it's been a long time now, with no high idle issue.

Link to post
Share on other sites

The coupe decided to idle fast again this morning. I immediately inspected and twisted the vacuum line that I had used for the SeaFoam. On CLOSER examination I could see just a few tiny dry rot cracks in the hose/line, and just pulled or tugged on the line and it disintergrated. I had some stock hose / line that I replaced it with - drove it about 5 miles and the problem seeems to be resolved....

Again thatksforthereplies folks :)

Nic

Link to post
Share on other sites

Nic, I expect we will be hearing more about this problem. Usually if a vacuum hose is leaking it leaks all the time and does not come and go as described in your posts. It could happen that way but is not likely. I spray vacuum connections and hoses with WD-40 where I suspect a leak. If the engine speed changes when you spray then you have found your leak. Some mechanics use a small propane tank, with a small hose attached to direct the propane to a specific spot, to check for vacuum leaks as described above but it is too risky for me.

Edited by Ronnie (see edit history)
Link to post
Share on other sites

Something does not sound right. AYTH/8064 Prom (revised 1990): Above 68C (156F) you should be "all in". In fact anything ove 56C and after 100 seconds fron start (25 seconds if coolant was above 69.5C) the idle should be under 700 stock.

You were stopped, right ? If moving the DFCO could command 1275 rpm (ish).

Edited by padgett (see edit history)
Link to post
Share on other sites

I was stopped, with my high idle problem.....not sure who you were asking......and yes, the IAC gets commanded to open depending on the vehicle speed. And I know you can't find anything to support my theory, Padgett, but I really believe that my low operating temps (160-ish) was somehow causing (possibly indirectly?) the ECM to command a slightly open IAC, which resulted in 1000 or 1100 rpm idle in P or N (or, subsequent 900-ish rpm idle in gear).

I would guess that the IAC opens up some with vehicle speed, so that when you let off the accelerator, the engine doesn't quickly slow the car down??? Just a crazy theory of mine...

Link to post
Share on other sites

If you shut the throttle competely at speed, you get a puff of raw gas/HC out the pipe. This is what they were avoiding.

A stock ATYH must think the coolant is below 32C to command over 940 rpm. Usually a high rpm problem when stoppped is tracable to a vaccuum leak or TPS error.

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...