Question about 1991 Isuzu Pickup

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1990 isuzu pickup 4cl often will NOT idle at very low rpms/under 15 mph unless I ride the brakes/E-brake and gas at same time. I know for sure I have a cracked ( in two places) exhaust manifold. The problem idle seems to be happening now more often as the manifold gets worse. It was tuned up about 4 months ago and has new, clean oil ( which it burns, but not like crazy) and fluids. It never over-heats and runs like a dream when it will stay running without constant gas. It also sems to happen more when the tank is less than half full, but the half full talk doesn't gaurantee anything. Has done it on a full tank, too. Is the bad manifold the reason for the idle/intake issues, or am I looking at a whole other mess? I don't know too much about cars or fixing them, but would love to imformed before I have it repaired (or not). Any info or advice is greatly appreciated. Thanks

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  • Isuzu Master
  • 20,706 Answers

This car EFI, or CARB, ill toss COIN, EFI gas.
what 4 cylinder, name it there are 7 used.
I'll now toss my coin land on GAS 4 cylinder engine. (in usa?)
is it racing too fast hot
or RPM too low hot.?

we cant guess what your statement above means.
but
the exhaust manifold cracks will cause the 02 oxy sensors to LIE,
to go lean (0volts ) this cause the fuel injection
to go RICH, (cause and effect closed loop rules)
and can idle too slow. (see that word SLOW)
the wrong word you used, after reading this vast times.

"NOT idle at very low rpms"
i decode this to mean?
NOt idle at proper low RPM (800 hot)
or spec 800 rpm , is more clear
that means the idle races hot.
this word is in all books on cars. engine RACES




IF true RACES it's not :
the exhaust crack, but can be if engine EFI slams in to limphome mode, do the flash codes show 12?
you never did those did you , bad idea skipping that. Google isuzu diagnostic jumper and read.
it's not he fuel tank ever,. not RACING.

what can cause any map based engine to race
well frankly LOTS:


but can be reduced to: (physics +)
1: throttle cables jammed. no slack. bad.
2: throttle valve jammed (gunk below it does that)(in the throttle body)
3: all vacuum leaks, (put huge list here, ask)
4: ISC or ICA valves stuck open
5: engine not reaching and holding 180f will cause #4 above to fail, naturally. bad thermostat. cause.
6: someone hacked your TB. (ask)
TB = throttle body.

vacuum leaks is an all day wall of text post
i refuse. but do have links to them.

Posted on Mar 14, 2017

  • 2 more comments 
  • Anonymous Mar 15, 2017

    what engine, gas or diesel
    and what size, we cant guess engines ever
    if in usa we can reduce,, gut guessing really does sux.

  • _-__-___-_
    _-__-___-_ Mar 15, 2017

    is it a diesel
    why must we ask ?
    here they all are,
    tell us now which 4 banger, first.
    are you in USA?


  • Anonymous Mar 15, 2017

    7, 4 banger's

  • Anonymous Mar 15, 2017

    every one wants help
    few know what's under the hood
    why? nor states country to lower the list.

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Posted on Jan 02, 2017

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volvo2103
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SOURCE: Fuel Gauge reads empty, but tank IS full

the float in your gas tank seems to have water in it....water is heavier than gas, that's why gas floats on top of water....try putting something like HEAT in it to dry up the water in your tank....

Posted on Feb 03, 2009

mackinbeats
  • 46 Answers

SOURCE: 88 Isuzu truck (4 cyl) has terrible idle/black exhaust

did you check for vacuum leaks probably a vacuum hose thats been knocked off or eroded and needs to be replaced.

Posted on Apr 11, 2009

  • 1 Answer

SOURCE: idle issues

I had the same problem and when I change the catalytic converter the problem was solve !

Posted on Apr 26, 2009

keithheavili
  • 410 Answers

SOURCE: Shake/Shudder while depressing the brake.

I just changed the brake pads and rotors on my father's 2001 Trooper that he recently purchased because they were shaking just like your were.  He bought it from a mechanic shop and they had put new pads on it but it needed new rotors as well.  If there is noticable groving on the rotors and new pads are installed it can create shaking, sometimes severe, when the brakes are applied.  It sounds like this is what has happened with your vehicle as well.  That being said, I don't consider it a huge safety issue to drive it until you get it fixed, just know that your braking will not be optimal and that it will take you longer to stop than if the brakes were working properly.  All that being said, get them fixed ASAP so you don't have to worry about it.  Who wants to mess with safety right?  Good luck, hope this helps!

Posted on May 18, 2009

  • 750 Answers

SOURCE: Rough idle engine ticking

check for a lose spark plug lead or cracked elecrod insulation on spark plug

Posted on Jul 09, 2009

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HI, i would advise to check the following areas for faults. replace any part that is fouled or malfunctioning.

1. Check the air filter- This device may be clogged or dirty. replace if visibly fouled.
2. Check the fuel pressure regulator- pull the vacuum hose of the regulator. if there is gas in it, replace the fuel pressure regulator.(if there is no fuel present in the lines, move on to the next check point)
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