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90 tracker distributor vacuum advance bad idling issues
#2
welcome banned! lol (G16a, gas hog, burns fuel like Huge V8 Chevy Blazer)
17mpg , is horrible 28 normal. 24-28 range. (is air cleaner clean and fuel filter, completing the tuneup)

Surge is the ECU telling you it lost control of hot IDLE.
bad IAT is very rare, G16a (1990) is a one wire, Intake air temp. sensor, that ? ECT fails 10x more that that,becauses runs 10 times. hotter, but both are robust. unlike say 02 sensor.
3screw is the IAC, Idle air, controller , 100% thermal. and must close above 150f. gasket missing sucks air, and all vacuum leaks cause fast idle. (if over powers iSC)
The vacuum advance has a diaphragm and all must hold vacuum or they are cracked, this is a standard test on all such vacuum actuators. pump 8 inches, hg. and hold, if not its bad.
15 is peck 400mm-GH, but i use 8"HG (200mm-hg) as its more gentle on very old parts.
first test the tool, with hose. put finger or a screw on end and see that the tool holds a vacuum, many dont'. then test any diaphram, there is. for leakdown test, its called.
one also looks to see the vacuum advance plate moves and holds,
compression is very good for 27 year old engine, amazing really.

MPG, good takes this:
CEL lamp on key, out running. if not, get the codes, (diag jumper) if not out the ecu is in limphome (failsafe) and will suck fuel like mad.
1: engine good, seems ok, check.
2: engine coolant reaches and holds 180f or more. must hold. or ECU goes nuts. IAC nuts and ecu never leaves cold start mode, sucks gas like mad.
3: good spark seems it is now, but does it advance like the book shows, gunning throttle. vacuum and mechanical advance, (ECU only does fuel not spark)
4: fuel pressure at spec , 34.1 to 39.8 PSI. (high end at sea level, pressure is based only on altitude.) see test port at fuel filter ,6mm screw.
pressure holds, at idle or cruise or gunned throttle. (unlike G16b)
5:fuel injector leaks, (air horn off TB, key off see it drip?, at the moment of key off (2man test)?
6: 02 sensor stuck at 0v all the time, runs rich bad 02 or exhaust leaks near it.
7: using a timing light test vac, advance and mech. advance if say the mech is rusted and stuck it will burn way to much fuel... advance exceeds 30degrees (left of scale ) or more gunned to high rpm parked, in Neutral. and see it advance aggressively.


AIR , is complex.. (only to point that so many possible)
fast idle is air leaks (aka, vacuum leaks) and all leaks cause fast idle, (ISC lost control) all do natural leaks or unnatural leaks ,all do.
its not cause of 17mpg, its just one more problem, as all do this old. many problems.
ISC leaks (aka stuck open), IAC leaks (both natural and wrong) by natural i mean air that was filtered at the air filter. IAC leaks when coolant never reaches spec,180f.
Un natural leaks are gaskets bad, like you just found and vacuum hoses cracked sucking air, even the brake booster can fail and let air suck in, vacuum will find any leak fast and easy.
TB base gasket leaking, some times the ISC on the TB is bad and leaks, its got gaskets there that can fail. or was molested at its rear screw.(hidden)
fast idle can be Gunk holding the TV open.
one of 3 throttle cables , 2 on MT. not set with 10mm slack spec, throttle cable or the cruise cable (option)
idle calibration set wrong. (throttle stop) causes ISC to loose control of idle, the ISC does this, via ECU commands. the ISC has 20 rpm, 800 and 950? the latter is idle up mode.
on 90,idle up is A/c on, heater blower on, head lamps on, or defrost on (option for rear glass, i bet is missing or dead)
800 rpm is spec,at all accessories OFF. all .

finding a working iSC on any 89/90 is an amazing site, and takes hard work to cure if out of control , the ecu is programmed to 800 rpm in a servo closed loop
'if it can get 800 ,it hunts (illegal today, ask Toyota the cost of that billions. fines)
hunting is unsafe it should close the ISC and hold it closed, but does not, it hunts in the blind and wrong attempt to gain control, (evil on a/t boxes never m/t) on m/t driver is always in control.

end air.
high mpg , can be brakes dragging or drive line bad, (bad bearings in trans,/axles/wheel bearings, etc) which Ill assume all is ok. so above is just answering for engine issues.
http://www.fixkick.com
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RE: 90 tracker distributor vacuum advance bad idling issues - by fixkick - 04-01-2017, 09:32 PM

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