Question about 1991 Isuzu Pickup

1 Answer

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

Posted by Anonymous on


1 Answer

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 20 achievements.


    An expert that got 10 achievements.


    An expert that got 5 achievements.

  • 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.
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.



6 Suggested Answers

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of.(from cars to computers, handyman, and even drones)
click here to download the app (for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017

  • 122 Answers

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

  • 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

  • 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

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

2 Answers

2016 Jeep patriot runs rough and won't go over 5 mph

Hi Joseph:
It should still be under warranty.
Take it back to the dealership.

Jun 26, 2016 | Jeep Cars & Trucks

1 Answer

1990 Isuzu pickup turns off at stop sign

If this is a petrol engine have a look at the brake booster leaking vacuum and running the engine too lean to idle. Test by allowing to idle with out your foot on the brake If applying brake pressure shuts the engine down ,replace the brake booster..

Jan 24, 2015 | 1990 Isuzu Pickup

1 Answer

Truck sputters and doesnt have power at lower rpms

Possible fuel pump about to die. They will work if revs kept up

Aug 12, 2012 | 1990 Isuzu Pickup

1 Answer

Broken brake line on 1990 chevy 4x4 pickup (K1500) broke and drained master cylinder. Front disc brakes/rear drum brakes. ABS system. Once brake line fixed what is the bleeding procedure that must be...

1990 Chevy 4.3 l engine runs rough at idle half the time-- sometimes it's OK, other days it's rough and can smell raw gas, as tho it's running rich... any ideas?

Nov 27, 2010 | 1990 Chevrolet K1500

1 Answer

2004 jeep grand cherokee special edition engine light on take foot off brake doesn't creep forwar, put foot on gas rpms go up but jeep only goes about 15 mph. THEN it worked just fine!!! Now the lights...

Get the check engine light checked you need to figure out the codes. Could be low on tranny fluid. If rpms go up and only moves for a short distance at 15 mph. Could be tranny fluid.

Mar 29, 2010 | 2004 Jeep Grand Cherokee

2 Answers

97 Nissan pickup will not idle

Visit the on-line store, know as reliable-store, they have the repair manuals. I'm sure you will get the solution of your problem.
Nissan Maxima Factory Service Repair Manual 1994 2009

Sep 08, 2017 | 1997 Nissan Pickup

2 Answers

I have a 1991 Isuzu pickup that will not idle. What can I do?

The first two things to check are vacuum leaks on the motor, and lines that have busted or off, also may be a leaking intake manifold gasket. Also, the idle control, it can go out from time to time. Hope that gives ya good starting point. A good way to check the manifold gasket is to spray along the gasket and see if changes the rpms.

Jul 21, 2009 | 1991 Isuzu Pickup

1 Answer

91 toyota pickup 4cl idles rough when warm when brake is pressed

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)
3. Replace the fuel filter and, check the voltage at th fuel pump. you should get 12V at the pump. if its lower than twelve, chekc the ground for corrosion as well as the entire wiring harness as well. all the way to the relay for fualts.
4. Check the Intake Manifold Gasket for worn or damged edges. this ware and tare will cuase leakge. replace this gasket if found to be fouled in any way.
5. Check the freash air intake hose. this hose may be clogged or damaged.
6. Last but not least, check the injectors for leaking seals and, correct pulse as well. replace any injector with a weak pulse or , leaky seal.

Jul 19, 2009 | 1991 Toyota Pickup

Not finding what you are looking for?
1991 Isuzu Pickup Logo

Related Topics:

41 people viewed this question

Ask a Question

Usually answered in minutes!

Top Isuzu Experts


Level 3 Expert

76846 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22246 Answers

Thomas Perkins
Thomas Perkins

Level 3 Expert

14384 Answers

Are you an Isuzu Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides