High idle revisited, just not so high anymore

[LarryK 87]

ok, have tried the suggestions posted and the results are, very little change

On start up the engine was surging to a very high idle, 1800+ RPM. Holds that idle for 3 - 4 seconds, then returns to normal

Reset ECM
reset IAC
rechecked all vacuum lines
disconnected the cold start circuit
the only thing i have done new to the car is repair my interior light circuit and re-install the fuse

Engine now starts with an initial idle now of 1500 - 1600 rpm,
return to normal with in 1 second, then immediatly starts to stumble, Exhaust smell ( and smoke) indicates the engine is running very rich, and now the dash is acting odd. RPM indicates 4500 - redline at an idle, Oil pressure indicates 45 - 58 psi and a red light ( but also jumps all over), Speed indicator appears to read correctly, and voltage reads 12.2 ( measured 13.0vdc at the battery termnals with engine at idle).

now it did this the other day on my way into work, and when i went out at the end of the day, Dash worked properly, and did not appear to be running rich, voltage indicated at 13.0 . start up was as noted above.

 

[vigman]

Sound like

BAD GROUNDS!


Check my "Getting Grounded" post.

Check the Batt to block ground.

Vig!

 

[LarryK 87]

have not yet checked the ground behind the ip, but i do notice there is NO braided ground strap between the frame, and the block, but the gnd cable goes from the batt to the block ( large gnd) and a smaller one from the batt. to the frame, but definatly no braid from frame to block, could this be an issue?
and i did just have the tranny rebuilt less than a month ago.
i guess up on the ramps tomorrow is the suggestion?
am pulling the dash cluster as well, and see if i can resolve the missing digit elements as well.

 

[vigman]

Oh Oh

When MY tranny was re done by that A$$

He put all the ground wires on the wrong bolt

and when the engine reved it YANKED the wires out of the crimped lug...

(&^$^&%($%%$(%)(%*&I@$!@%)#^# ER

So YES I would look at that FIRST

And there should be a braid where the small neg line comes from the batt to frame/chassis

and the braid jumps to the block there~!

Vig!

 

[WhalePirot]

The dash is one large LCD with a color plate that the lit areas shine through. Exchange the whole unit if the ground thing checks out.

The engine is stock?

The problems started just after the tranny work?

 

[LarryK 87]

the issue with the dash being wacko is new, the high idle at start began a couple of months ago.

 

[vigman]

Larry

Does the entire dash ( segments & all flicker )

or just 1 section flicker

or whats( a more precise description ) of the maildy.

Vig!

 

[LarryK 87]

no real flicker, just missing elements. In a much earlier post i had mentioned i mixed up the conductive foam pads, and have simply been living with it for the time being. Then this new weired out values issue.

OK, missing Gnd Braid, could not get to the mounting point on the block, but did attach a new gnd strap to an accessable point on the engine ( front most Exh. manafold bolt where alt support bracket attaches. Ran it back to the frame ground point, and using a dremel tool cleaned all mount points and re-attached, resistance shows as 0.0 on my DVM's 2k scale setting. Points measured where from:
new attach point to G-104, New attach to batt. cable, New attach point to valve cover bolts, Battery cable to various points on engine block, and heads, and new attach to G-101

Now G-201.... where is that sucker, Behind IP Left side near column, Have pulled the dash cluster, and looking up under, and through IP carrier, i can not seem to locate G-201. Is it hidden behind or above something?

and of course while i was under there i found why my ABS is fail, the wire from the L/F sensor ( a yellow and white pair after the connector has been ripped loose. Will chase that as time permits. It's Hot out there today !!!

 

[vigman]

A bit of misdirection here

IF memory serves
Look at the structral bracket supporting the dash ( drivers side ) where it bolts to the side pillar... you will find A ground there you might have to pull a bit of the carpet back to get this one. Its about where your toe would rest when driving, near the harness that goes thru the door.

... In addition there is one on a metal sub structure ( I believe ) under the dash to the right ( looking upside down..twds door) by the steering column.


Vig!

 

[LarryK 87]

well so far so good, engine running like it's supposed to , still starts with a high idle 1800+ rpm, then smooths out, dash is still missing digit elements ( center section only), but everything reads correctly, AND voltage actually indicates 13.5 - 13.8 consistanly now. Will have to see how it behaves in the heat of the day.

So whats left? none of the attempted fixes have cured the high idle @start up. BTW also reconnected the CS circuit, as that had no effect on startup.

On the good side, New Delco gas shocks will be here this week, and installed this weekend, New dash bezel has arrived, and waiting on the arrival of the new headlight switch, and fog light switch. This thing is actually starting to come togather. and may try and get it down to a svc shop and have thge AC evacuated, and retro'd to the new Enviro-safe refredge.

 

[vigman]

Well one down.......

Larry... check for tightness on the O2 sensor.

and ( I assume ) the car revs everytime you start..... I would block ( cap ) each vac line 1 at a time till the Zoom@start stops.

It's gotta be a vac leak somewhere.

The check engine light works?

Vig!

 

[LarryK 87]

checked the O2 while it was up on the ramps ( gotta love those rhinos), Check engine light works fine, no codes stored.

and yes, revs everytime it is started.

one thing i did notice this weekend, when you shut the engine down, you can hear a slight hiss ( read possible slight vacuum leak) at the coupleing of the main Vac line to the booster diaphram ( there is what appears to be a gasket/shim piece this does not appear to seat tightly, i could push it in a small amount and the leak stopped, let it go and i gound hear it again. Is this a serviceable item? and might this be enough to cause the startup problem?
It is the 90 deg plastic fitting that attaches to the brake booster diaphram front?

 

[vigman]

Air=RPM's

So you can do 1 of two things

Get some silicone seal and hit the connector.

Replace the booster grommet/fitting


As air leaks in it leans out the mix.. causing higher RPM.

I could see 1000 but 1800... that's got me curious...

and after a period of time it's fine...

You start... it will idle & drop all by itself?!

I'm thinking stuck IAC... or something that makes the engine THINK it needs more....then the ECM wakes up and sez WHOOPS..My BAD!


When the cars up to temp.. it idles fine...right?

You restart in 5 min and you get the Vroom ( 1800) factor.

How much of a time period before it settles down?

This has me going... I would still try the isolate the vac lines.

Vig!

 

[LarryK 87]

Since i re-did the grounds, Running idle is fine ( surging is gone for now ), the high start up idle remains. Like you i suspected a sticking IAC until i found i could stop it by simply putting it into diag mode, disconnect IAC, then key off, reconnect. It will always start fine then, one time only.

The High idle is brought down with in 1 -2 seconds after start up
( warm or cold).
it seems the Hotter the engine, and ambient temp, then the higher the start up idle, yesterday stopped at mail box, restart gave me a 2000 startup rpm then right back to normal with in 1 -2 seconds.

Its almost as if, like you say, the ECM sets the wrong IAC step for startup, suddenly see's it is wrong and then corrects it.