low idle, stalling

[Ryan]

Let me start by saying I really do not know a whole lot about cars haha so bear with me. But anyways I have a 5spd 2000 isuzu rodeo that giving me some problems:

-First off if its been sitting for a while (a few hours) and I start it up and go right away it bucks really bad and barely accelerates. However, if I let it idle for a few minutes it runs fine and if its only been sitting for a short period of time it starts right up and drives fine.

-Next problem is very unpredictable and has only happened a few times but did it to me again today. Anyways the idle has always been kinda low (around 400 rpm) but today I was sitting at a light in neutral and felt the car start to shake. I looked at the tach and it was hovering at zero rpm. Made it to where I was going and when I started heading back home it seemed fine again. However about halfway home I felt the shaking again at a stop sign. I tried to take off this time and it stalled. I started it back up and it bucked really bad and was barely accelerating at all and it crawled about halfway through the intersection until it starting picking up speed. Repeated this for the next 4 stop signs and I somehow managed to make it home. Got home, shut it off, told my dad what it was doing, we hopped in and took it around the block a few times and it ran fine... Go figure.

[LHOswald]

check for fouled spark plugs, make sure your getting enough air into the engine (IT NEEDS TO BREATHE DAMNIT!) and check to make sure your fuel pump is pushing enough gas as well (could also be injectors). whens the last time an oil change was done or plugs were replaced? plugs is most predominant but thicker dirtier oil will cause the engine to have to push through more goop to accomplish the same task. also check distributor\cap+rotor

welcome to the site!

[RITmusic2k]

A vacuum leak could also be the culprit. IAC (Idle Air Control) valves or the hoses that attach to them can fail and cause erratic idle. So, I take it you were not able to raise the engine revs with the gas pedal when it started idling low / compensate for the hesitation by giving it more gas than usual when you were moving?

[Ryan]

check for fouled spark plugs, make sure your getting enough air into the engine (IT NEEDS TO BREATHE DAMNIT!) and check to make sure your fuel pump is pushing enough gas as well (could also be injectors). whens the last time an oil change was done or plugs were replaced? plugs is most predominant but thicker dirtier oil will cause the engine to have to push through more goop to accomplish the same task. also check distributor\cap+rotor

welcome to the site!

Im due for an oil change fairly soon but as far as the spark plugs I have no idea when they were last replaced. I've only had this truck for about 7 months, but something worth mentioning is that I know it sat for QUITE a while. It was my dads boss's old work truck that he just kinda stopped using. When I first got it I changed the oil and all that good stuff and it ran great. However, these problems just started over the past couple months. Ill definitely get the oil changed asap and take a look at the plugs too.

A vacuum leak could also be the culprit. IAC (Idle Air Control) valves or the hoses that attach to them can fail and cause erratic idle. So, I take it you were not able to raise the engine revs with the gas pedal when it started idling low / compensate for the hesitation by giving it more gas than usual when you were moving?

The first time this happened and I noticed the shaking and low rpm I stabbed the gas and there was some slight hesitation. When the rpm fell back down the needle settled just about at zero rpm again. It was definitely on the verge of stalling but I didnt actually have to hold the gas to keep it from doing so. I was able to launch fine though and made it to where I was going just up the street from that point. It was still idling extremely low when I pulled into my parking space. When I started it back up later the rpm was back at its normal 4-500 rpm. About halfway home things got bad again and at a stop sign I felt the shacking and saw the needle hovering just above zero again. But this time when I tried to launch it would stall or buck and not accelerate at all even when I had the gas practically floored in first gear with the clutch all the way out. Ill be sure to check out those hoses though, like I said this truck sat for a long time and the hoses could have dried out causing them to crack when it was finally driven again.

[fa22raptorf22]

Yeah, 4-500 rpm is way too low. Id say the IAC/IACV is your culprit.

A normal idle should be at least 600 in my opinion.

[theholycow]

Yeah, 4-500 rpm is way too low. Id say the IAC/IACV is your culprit.

A normal idle should be at least 600 in my opinion.

That's totally dependent on the engine. A GM V8 should idle smoothly at 500 or less.

A 2000 Isuzu Rodeo V6, which my wife has, definitely idles higher, IIRC 750 or more.

Here's a list of your problems:
1. It sat unused for a while. That's really tough on a vehicle.
2. It's a 2000 Isuzu Rodeo. That's really tough on a vehicle too.

[Ryan]

Alright thanks for the help guys, Ill check out everything you suggested.

[Swimmerboy]

What's your A/F ratio? Check for vac leaks also. Are you throwing any codes?

[AHTOXA]

A GM V8 should idle smoothly at 500 or less.

Not necessarily. Mine idles around 700 to 750. Now if I'm launching and it dips to 500 I can't feel any shaking, so it technically could idle that low. However I haven't seem many cars where normal idle is below 650 or so.

[theholycow]

Not necessarily. Mine idles around 700 to 750. Now if I'm launching and it dips to 500 I can't feel any shaking, so it technically could idle that low. However I haven't seem many cars where normal idle is below 650 or so.

Hmm...maybe not high-performance ones with aggressive cams.

The GM Vortec V8 series in trucks idles at 500-550.

[Rope-Pusher]

ZERO RPM? You do know that if you can get it to idle in negative numbers it will actually make gasoline, right?

[LHOswald]

That's totally dependent on the engine. A GM V8 should idle smoothly at 500 or less.

my buddys legacy with a boxer 4 idles that low

[watkins]

Boxers are by their very nature some of the smoothest running engines

[LHOswald]

Boxers are by their very nature some of the smoothest running engines

QFT

[ElectroGhandi]

Hi Ryan. I also have an Isuzu Rodeo, but mine is a 94. However, we have the same engine (assuming you have the V6) and mine idles at about 1200 rpm. Your low idle could be due to:
-Cylinder misfire
-Dirty fuel injectors
-Water in the gas tank

You might also just need a tune up. theholycow and I are the resident Isuzu Rodeo people. Hope to see you around!