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89 Tracker Over-revving on start up
12-06-2018, 07:40 AM
Post: #1
89 Tracker Over-revving on start up
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?
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12-07-2018, 08:33 AM
Post: #2
RE: 89 Tracker Over-revving on start up
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.

(12-06-2018 07:40 AM)WizBang Wrote:  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?

http://www.fixkick.com
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12-08-2018, 02:05 AM
Post: #3
RE: 89 Tracker Over-revving on start up
Thank you. Weekend is coming. I'll check it out.

Sorry, DASH pot? New term to me Huh
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12-08-2018, 03:57 AM
Post: #4
RE: 89 Tracker Over-revving on start up
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)
[Image: TPS-testing.html#8v-gage]


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 !

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12-08-2018, 12:50 PM
Post: #5
RE: 89 Tracker Over-revving on start up
Excellent, thank you.
Lots to check out here and will post what I find
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12-10-2018, 11:22 PM (This post was last modified: 12-10-2018 11:24 PM by fixkick.)
Post: #6
RE: 89 Tracker Over-revving on start up
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.

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