Question about 1990 Mercury Grand Marquis

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Engine stalls after cold start-up & release from high speed idle

1990 mercury g/m-5.0L-V8-EFI, mileage-86,000mi, Ignition & fuel systems appear OK. No service light,no codes. After restart at high speed idle ,engine will reduce rpm & continue to operate ,but at times will stall unless accelerator is depressed to maintain rpm. After warm-up engine is OK. Cold start is the issue. Please help. Thank you.

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  • bjtoy13 Mar 07, 2009

    Att: Auto Dr. & Mikem700- thank you, problem solved using both solutions. Your attention is appreciated. bjtoy13

  • Anonymous Mar 14, 2014

    Have6a12 engine, idle speed to high, how do I reduce it? Accelerator cable not tight and idle screw on throttle Boyd backed off, idle speed still to high



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I had a similar problem.  I found the filter cartridge below the pcv valve had carboned up, and after the crank case pressurized, oil was forced out the pcv supply line to the throttle body.  The idle air control valve solenoid got oil in it and caused my problem, but only when it was cold.  The pcv cartridge is accessed by removing the pcv valve and the rubber fitting that the pcv valve mounts in.  It can then be fished out with a pick set, and it is a pain because you can't see it, but you can get you hand back there.  I hope this helps you.

Posted on Feb 28, 2009

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Well the first thing that comes to mind is the idle air control valve located on plenum/throttle body. that valve controls the air flow to engine when its at idle. could remove, clean shaft with carb cleaner and lubricate. and see if that makes any difference. valve may need replacing but this is a good test

Posted on Dec 07, 2008


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I have a 90 geo prizm I have changed the plugs ignition control module fuel pump and fuel filter the car runs for a few minutes till at normal temp then shuts down when put it in gear any suggestions

wow , year, body name Prizm stated, Prizm is a TOY corolla.
but not the engine, or trans.
my wild guess this is the TOY 4aFE engine. 1990
i have 50 guesses for you, would you like me to toss dice and spit one out? or would you like to try real diagnosis.?
your call.
using real tools, lacking tools, its impossible to do this.

sorry. EFI systems and ENGINES are complex with huge numbers of failures, possible.

sounds like an auto trans there, shifting from Park to drive..
Best is to say DRIVE,
and when you do that a huge load is put on the engine.
and if its stalls its cause by 1 of 2 reasons.
idle controls dead;
or engine is weak.
so if you use the fast right foot trick you lean which it is.
is engine rpm at spec, hot ?
is engine rpm at 800 or more in park.
when you shift to drive, the rpm most hold at 800.
if not the engine is weak for sure if the fast right foot cant make car move.
if the trick above works, i can drive using the fast foot trick, then we do idle speed controls tests.
if not (its misfire, caused weak engine)
the engine is weak, top reason misfire or under injected.
under injected is lean and bogging engine, and stalls.
the 50 other causes. starts now. or up to 10 more tests.

starts ok.
idle cold ok, no misfiring? or engine shaking
can you drive it dead cold???????????????
then are you saying only the hot engine , shifted to drive
causes a stall but not driving a cold engine>?

if all that is true, then use the hot right foot, happy foot.
you foot can in fact bypass the idle controls of all EFI engines made (gas).
This trick adds air and the ECU adds fuel matching your added air.
see how this magic works.?
so does it work. this trick.? i can drive now it a happy right toe?
THE key answer, to diagnosis.

and if you hear /feel or see misfire, that too is key and no blind net bunny can see this.
it must be seen and reported.
spark plugs gaped to spec>/? not guessing?
new spark plug wires, on a car this old the original are all DOA.
compression at 150PSI or more , at sea-level to 1000'feet.
if not , say so, and the readings as WOT. (open the throttle to do compression tests are its all just a wasted effort)
cap and rotor new, (26year old parts here are junk)

also battery voltage need to be 13.3v to 15vdc running.
if not ?and the alternator is dead, the voltage drops and EFI stalls the engine, so we always check system main voltage on all cars the run bad, and fuses.

we also check fuel pressure ! on all engine that flood or bog.
and the flash codes, (magic 1990 jumper clip flash codes)

Apr 25, 2016 | Geo Cars & Trucks

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Lost power in celsior v8

what country
4.0 L 1UZ-FE V8 its a fuel injected V8. used in Lexus LS400s in USA.
i restore old cars and 1990 is old.
lost power can be misfire , does it do that hot /cold or both engine temp? loss power, under what coolant temps.
so if the tranny dont slip or brakes drag. (car rolls easy) then
the engine is sick , this is an EFI engine.
on all old engines. Get a real FSM, for sure.!!!
  1. check compression, first. 150psi or more. good on all 8 (W.O.T)
  2. tune it up, wires plugs, cap ,rotor.. filters. (all)
  3. Ignition timing: 8 -12deg BTDC @ idle (Transmission in neutral position)? 1-8-4-3-6--7-2, firing order sparks wired right?
  4. I then make sure fuel pressure is at spec,
  5. at the same time. the classic injector leak down test.
  6. at the same time, the classic, injector balance test.
  7. With all that good the EFI system has hope.
  8. I then check the ECU for DTC errors, (flash codes )an address all those.
  9. the eng. thermostat get to 180F or more fast and holds !!!
  10. if clean the MAF a dirty MAF, will cause lean and lean causes bogging and huge loss of engine power
  11. does the engine hold closed loop. at idle and at 2500 rpm in neutral (hot engine) id bet not.
  12. no scan tools so all you have is a blinking CEL lamp test so do that check. The check jumper wire.
  13. on these old dogs, i must check every sensor by hand due to no SCAN tools in 1990
  14. thats enough, for now. I see wasted spark coil packs, got misfire?

Feb 18, 2014 | Toyota 105 Cars & Trucks

1 Answer

1990 jeep wrangler runs rih won't stay running replaced map sensor and temp sensor

which engine,? the have up to 3 choices.
what are the full symptoms,
did you do the full listed 60k mile tune up on car?
sparkplugs,wire, cap rotor/filters? no engine runs right with bad spark
unless it's a diesel.
starts good
runs good or bad hot or cold engine
idle at 800 RPM hot?
stalls> when hot and cold engine
lost of power

only stalls , but runs perfect even up hills, at wide open throttle.
fresh gas, or 1 year old?fuel.
can your fast right foot , save the stall, and easily?

ok stalls 101.
1; lost 12vdc to EFI system.
2: lost engine compression.
3: lost spark.
4: lost fueling or floods
there is a simple test for each.
do you want more guesses, or how to do tests.
can do both, but my guessing fails 99 /100 times.

tune it up
do the right foot test. those are always first. on stalls.

Feb 05, 2014 | Jeep Wrangler Cars & Trucks

1 Answer

Engine runs rough and gets worse when accellerating

Rough idle, stalls or
hesitate on acceleration :
.Spark plug faulty
. High-tension cords faulty
Ignition problems:
• Ignition coil
• Igniter
• Distributor
. Incorrect ignition timing
Vacuum leaks:
. PCV valve and line.. .
. EGR line..
. Intake manifold.
• Throttle body
• ISC valve
• Brake booster line

• Throttle body
• Brake booster line
. Incorrect idle speed
. Reset timing
. Adjust valve clearance
. Check fuel system . Check air cleaner
. Incorrect valve clearance
. EFI system problems
. Low compression

Dec 12, 2013 | 1989 Toyota Camry

1 Answer

Increase then decrease idle when engine is cold especially

cold engine idle surge. (problem)
RPM range of surge not stated
300-700 or 800 to 1500? (range is critical to diagnosis)

bad fuel
running summer fuel in winter (running old fuel?)
needs a tune up bad, see the list in the operator guide.
idle speed controller,sticking or EGR valve same. (clean them)
location not stated, so cant guess about local air temps.?
no other symptoms, lack of engine power? etc?
was it ok last week, or better, when was the last time it was OK?
1week, 1year?
surge , causes, on a tuned engine might be:
1: too lean. so lean the ISC can not control idle. rpm low, stalling
2: too rich, flooding, stalling, spark plugs foul (look at them)
3: weak compression in 1 or more cylinders.
4: bad spark.
5: air leaks, in the plenum causing , ISC to lose control.
why high RPM?

well that means it fails hot too.
and there is a simple tests. for hot surge.
is engine fully hot? 180F and holds solid there?
say rpm is about 800
and you turn on head lights, heater fan and (not AC) and defrost.
the RPM must hold or the ISC is failing.
ISC -= idle speed controls. (all EFI has this function)

Oct 28, 2013 | 1996 Honda Prelude

1 Answer

1990 VW Fox Fuel/Engine Miss

change air filter.and fuel filter. replace plugs and wires.check tires air pressure.

May 30, 2009 | 1990 Volkswagen Fox

2 Answers

4 cyl Engine starts and idles ok...give it throttle and it dies

I need to get a clear mental picture of what exactly is happening.

With this said, you stated that the car "runs fine" until warmed up.

Q: When you start the car when cold it idles fine?
Q: If you allow the car to idle until "fully" warmed does the car stall?
Q: As the car begins to warm up, Does the RPM fluctuate abnormally?
Q: Does the car Only stall when you press on the gas pedal or does it stall just sitting and idling in addition to pressing the gas pedal?
Q: If you can drive it while cold does the car stall during acceleration when warm or only at Stop Signs / Lights?
Q: If you wait 20min or so, can you start the car again?
Q: How many miles are on the car?

Mar 27, 2009 | 1995 Toyota Camry

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99 Grand Marquis won't stay started when engine cold.

Here is the most common cause of this stall, it is the idle speed control air-bypass valve and throttle valve, they get full of gunk over the miles and cause idle issues (stalls) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake

Oct 29, 2008 | 1999 Mercury Grand Marquis

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