89 Tracker Over-revving on start up

[WizBang]

Since I did my tranny drop/clutch swap/oil-pan repaint my 89 Tracker (8V manual 4x4 2 Dr) it has been racing up to about 4000rpm on start up. It holds this rpm longer when cold (approx 2-4 seconds). It was the worst when I first started the engine after being off for about a month while doing the tranny drop, etc. That kinda freaked me out and I turned the key off after about 5 seconds of it racing at 4k. I started it again after checking the throttle cable hadn't jumped, etc. and it still did it and I shut it off again after about 5 sec. On about the 3rd or 4th start it finally dropped down to about 1500rpm after a couple seconds.

Wondered if the vacuum hoses got stretched and one cracked when the block was being tipped forward/back during the tranny re and re but I ran my fingers along and around
each with the engine idling to see if there was an rpm change. Nada

Any suggestions or suspicions?

[fixkick]

4000RPM , the DASH pot device on the throttle is set wrong. ? may be.
first tie back the dashpot see if starts at 1000 to 1500 rpm always cold, per the IAC air openings in the base of the TB,
for sure its vacuum leak issues, 89 is old and there will be issues here, lots.

The dash pot spec , is 2500 on hot engine, if you engage the DP falsely and forced, one way to do that is start car hot.
pull the DP hose see it extend, and plug the tip of this hose with a golf tee or spare screw that fits.

the DP then extends,and it end has screw adjuster you set for 2500 RPM hot
once this is done, the DP then when cold does not go too fast. '

THE ECu retacts the DP, by command and short delay in few seconds. after keyed start.(hot or cold)
The IAC in the base is open when cold, and is the major air leak that sets cold start idle speeds.
make sure the DP is not sticking in some way.
the total air is TV + IAC +ISC + DP. 4 sources of air, I no vacuum leaks on hoses.


hoses can sure be bad this old, seen 91, with hose look like turning to TAR, nasty hoses. had 2 do that 1 on MAP hose,.

good luck and thanks for sharing.

Since I did my tranny drop/clutch swap/oil-pan repaint my 89 Tracker (8V manual 4x4 2 Dr) it has been racing up to about 4000rpm on start up. It holds this rpm longer when cold (approx 2-4 seconds). It was the worst when I first started the engine after being off for about a month while doing the tranny drop, etc. That kinda freaked me out and I turned the key off after about 5 seconds of it racing at 4k. I started it again after checking the throttle cable hadn't jumped, etc. and it still did it and I shut it off again after about 5 sec. On about the 3rd or 4th start it finally dropped down to about 1500rpm after a couple seconds.

Wondered if the vacuum hoses got stretched and one cracked when the block was being tipped forward/back during the tranny re and re but I ran my fingers along and around
each with the engine idling to see if there was an rpm change. Nada

Any suggestions or suspicions?

[WizBang]

Thank you. Weekend is coming. I'll check it out.

Sorry, DASH pot? New term to me

[fixkick]

sorry DP or this dashpot is only on all 8v G16s,
it is also called the fast idle vacuum servo) it runs for 3 to 15 seconds, mostly.
the word is old and silly, its neither DASH nor a POT.
in the old days of carbs they hand this same name device that is either a shock absorber or is device to raise idle with AC turned on.
then in 1989 it is now full time device, that is only on 8v for preventing liquid fuel puddling under the TB plenum box below.
see here 91. (89 is near)



here is my DP page the DP adjuster is seen here just to the right, of the DP plugger.
http://www.fixkick.com/IDLE-AIR/Dash-pot.html

fast idle is always air leaks. too many.
lots of causes. huge. really, were a vacuum exists air wants to leak badly.
TB throttle valve plate gummed up, as it hits the bore is ticks, so force it closed by hand see TV close bingo it was stuck.
the DASH pot retracts , just watch it if it retacts in your 4 stated seconds, and retracts leaving a gap, then DP is OK> unless rpm is only 4000 DP active.
next is ISC sticking top of TB see 2 wires to that? ISC is how ECU keeps 800 RPM hot. it is the idle speed control regulator
the IAC in the base of the TB is closed at 150F, if not it is Bad.
but cold the IAC will be near open or fully open at or 0.060" at -10f (using numbered drills shanks by me in freezer) only I have this data.
http://www.fixkick.com/sensors/tests/IAC-T-tests.html

next is vacuum leaks, for sure if hot idle is not 800 you do have leak.
hot engine 180f+ only 2 air paths exist, ISC and TV,. all others must be closed.
all vacuum leaks the MAF sees it and measures it and adds fuel (to match) and idle always goes higher on this car.
what happens at 180F? idle?
good luck to you !

[WizBang]

Excellent, thank you.
Lots to check out here and will post what I find

[fixkick]

all Excessive vacuum leaks cause excess idle speed,
and is normal cold, 1500 par.
once hot the IAC closes 100% leaving only hot air paths.
if there is vacuum leak the ISC is closed to ready 800RPM hot idle. if the leak is huge
the ISC can not close more and may even hunt the ISC and idle hunts.
all vacuum leaks most be removed, mostly hoses bad. or even fell off?
or brake vacuum booster can crack and will suck huge air.
I pinch hose, or remove them and plug them to prove that path does not leak air.(vacuum leaks)

even the idles speeds set wrong by others, fiddling that TB idle stop screen wrong.
or gunk under the TB TV throttle valve plate or all cables to the TB not set with spec slack.

[WizBang]

Sorry.  After a long winter's nap I'm back at trying to fix this problem.  (Tracker only gets used during the hunting season and for pushing snow)

Checked Dash-Pot and, although a bit sticky on initial release, it opens with vacuum and holds the vacuum.

So I replaced all of my 1/8" ID vacuum tubing with new.  On start-up I had the same over-revving issue.

Pulled vac hose between EGR modulator and dash-pot and it had a lot of carbon coffee grounds in it that may have affected vacuum, but I suspect not.  Blew them out.
Decided to pull dash-pot (which I had removed, and repainted last year before the problem started ...hint...hint) and immediately noticed that the two bolts weren't very tight.  Hmmm......  I suspect this is my problem.  I used hi-temp gasket sealer when I put it back on, lightly tightened the bolts, and likely forgot to re-tighten the bolts after it had cured.  The leakage here would make perfect sense in explaining my over-revving issue on start-up.  Also curious to see if it addresses my 1800rpm idle, hot!

Wondering what sheet gasket material to buy for doing the job properly this time??

[fixkick]

Sorry.  After a long winter's nap I'm back at trying to fix this problem.  (Tracker only gets used during the hunting season and for pushing snow)

Checked Dash-Pot and, although a bit sticky on initial release, it opens with vacuum and holds the vacuum.

So I replaced all of my 1/8" ID vacuum tubing with new.  On start-up I had the same over-revving issue.

Pulled vac hose between EGR modulator and dash-pot and it had a lot of carbon coffee grounds in it that may have affected vacuum, but I suspect not.  Blew them out.
Decided to pull dash-pot (which I had removed, and repainted last year before the problem started ...hint...hint) and immediately noticed that the two bolts weren't very tight.  Hmmm......  I suspect this is my problem.  I used hi-temp gasket sealer when I put it back on, lightly tightened the bolts, and likely forgot to re-tighten the bolts after it had cured.  The leakage here would make perfect sense in explaining my over-revving issue on start-up.  Also curious to see if it addresses my 1800rpm idle, hot!

Wondering what sheet gasket material to buy for doing the job properly this time??

tsure what you mean by dash pot the DP has no direct vacuum to TB, at all it is just bracket only. and vacuum nipple that can leak. no gaskets here.

the DP is that device on 8v that  openss the throttle cold started for 3 to 15 seconds, then release and the shift on the PD plugger retracts from the throttle valve and has and air gap there running at all times (not first startup)
the only gasket-ed device that can leak vacuum (easy fix, not hard intake man)
iS EGR MAIN. (and all hoses sure) the hoses can  be pinched to find if any hose leaks or and device an the end leaks. when engine races too fast..
The egr runs supper hot  cruising (exhaust) and can easily wreck any simple paper gasket, here






Even sludge under the TV plate can case fast idle.  so force  it closed by hand hard, if it moves and idle speed drops the cable is too tight or the TV is blocked.
when the EGR hot gasses hit the PCV Gas cloud under the TB that makes sludge.
the PCV valve can stick open or be wrong valve for 1.6Liter. and cause fast idle. (leaks vacuum) or worse a cracked hose.

no AT modulator to leak it  is a MT 5speed.
no extra  TB gasket to leak no AT mean no TB base heater.
so the air vacuum leaks are only gaskets. and hoses on this car. and 2 devices with diaphragms.  and 2 VSV valves not cracked or stuck open.