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Discussion Starter · #1 ·
I've got a 2004 Tacoma with the 2.4L w/ the 5-speed and I just can't seem to get rid of a rough idle when it's warm. It's not terrible but does feel like it's getting slowly worse - I've cleaned out the IAC which I think helped a little. (Could be my imagination+wishful thinking) I also changed out the motor mounts, spark plugs, and fuel filter to no effect. The truck has 60k miles on it and has never even given me a CEL once. No other signs/symptoms, and I don't see anything immediately hinky on my autel. Any thoughts? Can an ignition coil go bad without a dash light coming on?
 

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Mambeau / Admin
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If it only happens when the engine is warm there's a chance you have an electrical connection that either shorts out or gets loose when something heats up and expands.
 

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Discussion Starter · #3 · (Edited)
If it only happens when the engine is warm there's a chance you have an electrical connection that either shorts out or gets loose when something heats up and expands.
Any ideas where to start? I looked through the live data with my scan tool, and all the sensor readings appear normal. Short and long term fuel trim are good (±.05%), rpm is at 690-700 when up to temp. No misfires counted on all cylinders. It's almost like she should be running great but just isn't... I'm at a loss
 

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Mambeau / Admin
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Is this Taco bone stock, or have you made any fuel / ignition / whatever modifications to it? If you've made any mods, what were they?

Thanks for the clarification about having checked the data / signals using a scan tool.

You mentioned the rpm's being on-spec (690 - 700) once the engine's warm. What's the rpm range before that (while the engine's still relatively cold)? There may be a clue in that.

An intake air leak might explain it - especially if there's some leakage point that doesn't open up until it's heated.

Have you checked and adjusted the timing? Was there anything (a change; a mod; whatever) that occurred just before this behavior began?
 

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Mambeau / Admin
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Here's another angle ... 60K-miles is a remarkably low mileage figure for an 18-year-old engine. It makes me wonder whether something mechanical is gummed up / corroded / whatever because of low usage, and this mechanical issue is affecting engine function when warmed up.

This would explain why the fuel / ignition systems seem to be working fine but the engine isn't idling quite right.
 
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Discussion Starter · #6 ·
Is this Taco bone stock, or have you made any fuel / ignition / whatever modifications to it? If you've made any mods, what were they?
It is bone stock, single cab w/ 5 speed manual. If you can think of an option it doesn't have it : alarm, clock, power windows, cruise control, power locks, etc

You mentioned the rpm's being on-spec (690 - 700) once the engine's warm. What's the rpm range before that (while the engine's still relatively cold)? There may be a clue in that.
I don't remember - I'll scan it again first thing in the morning for that, though it does run smoother before she warms up.

Have you checked and adjusted the timing? Was there anything (a change; a mod; whatever) that occurred just before this behavior began?
it only has 57k miles on it, so I've never thought to check the timing. I'll have to see if it has a belt or a chain. (I hope it's a chain lol since I'm pretty sure the 2.4l is an interference unit) as for changes, the only thing I've done is clean the IAC in an attempt to rectify the rough idle.
 

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Discussion Starter · #7 · (Edited)
You mentioned the rpm's being on-spec (690 - 700) once the engine's warm. What's the rpm range before that (while the engine's still relatively cold)? There may be a clue in that.
This morning she started right up, initial rpm is ~1300 rpm, and slowly but surely drops in around 800 until it completely warms up. (At which it pegs right at 700)

Ignition advance is ~14 when warmed up.

I did notice the air flow rate never got above ~.1 when accelerating up to 50mph, yet the data range for listed is 0.00-1.44. what should the normal values for this be? It just seems weird to me that the "calculated load value" for the engine is 80% but the MAF only registers an 8% capacity intake volume?
 

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Discussion Starter · #8 ·
Here's another angle ... 60K-miles is a remarkably low mileage figure for an 18-year-old engine. It makes me wonder whether something mechanical is gummed up / corroded / whatever because of low usage, and this mechanical issue is affecting engine function when warmed up.

This would explain why the fuel / ignition systems seem to be working fine but the engine isn't idling quite right.
What do you think being gummed up would affect warm idle and not cold? This is my first Toyota and I am not familiar with their quirks and oddities.
 

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Mambeau / Admin
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What do you think being gummed up would affect warm idle and not cold? This is my first Toyota and I am not familiar with their quirks and oddities.
I don't know - I'm just spit-balling ideas because the situation is confusing.

The reason I mentioned some sort of mechanical issue is because you're not seeing any codes being thrown. If everything's working this means the ECM 'thinks' everything (fuel / ignition / trim) is fine. Unless the ECM gets a bad signal reading from the knock sensor it has no idea whether or how well the (mechanical) engine is running.
 

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You may be onto something with the maf reading. Can you shoot some pics of the scan tool data?
How does it run otherwise?
With the mileage, check inside valve cover for it being nasty. Lots of low speed operation they may Have extended the service intervals out and you could be experiencing a loose timing chain from warn guides or a weak oil pump
 
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Discussion Starter · #11 ·
Sorry for the delay in responding, I managed to catch the 'Rona this week and I did not feel up to touching the truck lol. I do have good news though - I replaced the IAC valve and she purrs like a kitten now!

I spoke to a friend of mine who runs an euro/import repair shop and he says with IAC valves he always replaces them because you can't really clean them all the way - and he also thought that might be what my issue was. Ended up being about $150 including shipping, so not too bad I suppose?
 

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Mambeau / Admin
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Glad to learn you seem to have solved the rough idling. Thanks for reporting the results and reminding us all that cleaning out an IAC doesn't necessarily make it "like new".
 

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I've got a 2004 Tacoma with the 2.4L w/ the 5-speed and I just can't seem to get rid of a rough idle when it's warm. It's not terrible but does feel like it's getting slowly worse - I've cleaned out the IAC which I think helped a little. (Could be my imagination+wishful thinking) I also changed out the motor mounts, spark plugs, and fuel filter to no effect. The truck has 60k miles on it and has never even given me a CEL once. No other signs/symptoms, and I don't see anything immediately hinky on my autel. Any thoughts? Can an ignition coil go bad without a dash light coming on?
You could check your plugs and your plug wires! Hope it helps mine started to shake and it got worse so I checked my coils but they seem to be good so I put new spark plugs in the dubble pole which mine is a automatic 6 cylinder, which I didn’t know it does call for double pole which I put in my self it help alot and the shake was their on idle at a red light not bad and changed all my wires and I have no more shake, I hope it helps! I hope it nothing too serious!
 

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Discussion Starter · #14 ·
You could check your plugs and your plug wires! Hope it helps mine started to shake and it got worse so I checked my coils but they seem to be good so I put new spark plugs in the dubble pole which mine is a automatic 6 cylinder, which I didn’t know it does call for double pole which I put in my self it help alot and the shake was their on idle at a red light not bad and changed all my wires and I have no more shake, I hope it helps! I hope it nothing too serious!
I solved my idle issue by replacing the IAC valve, but I had already replaced the spark plugs recently. Also I don't have distributor with individual spark plug wires, is that what you mean? My truck is coil-on-plug and the ignition coil connectors don't seem to be on any sort of pigtail so I'd have to change the engine harness or custom fab something if one of them broke.
 

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I solved my idle issue by replacing the IAC valve, but I had already replaced the spark plugs recently. Also I don't have distributor with individual spark plug wires, is that what you mean? My truck is coil-on-plug and the ignition coil connectors don't seem to be on any sort of pigtail so I'd have to change the engine harness or custom fab something if one of them broke.
Oh ok I gotcha, at least your solved the problem!!!
 

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I solved my idle issue by replacing the IAC valve, but I had already replaced the spark plugs recently. Also I don't have distributor with individual spark plug wires, is that what you mean? My truck is coil-on-plug and the ignition coil connectors don't seem to be on any sort of pigtail so I'd have to change the engine harness or custom fab something if one of them broke.

Where did you end up ordering from? Or did you pick up the IAC Valve from a local parts store?

'Cause Autozone wants $207.99 but has lifetime warranty & Rock-Auto has it for $120.79 but with a 3-year warranty [Not sure how you would submit a claim]
 

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Discussion Starter · #17 ·
Where did you end up ordering from? Or did you pick up the IAC Valve from a local parts store?

'Cause Autozone wants $207.99 but has lifetime warranty & Rock-Auto has it for $120.79 but with a 3-year warranty [Not sure how you would submit a claim]

I ordered it through Rock Auto - SMP was the brand. I've ordered engine mounts, coils, and other stuff from that brand and it seems high quality and value.
 

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How ironic-
I was thinking about going with Standard Motor Products [SMP] too.

I'm thinking about starting with the manual-tranmission mount first and save the motor-mount replacement for the spring/early-summer...
Cause to me, OE Toyota parts are way-over priced in general...

Anyway, How hard was it to replace the motor-mounts?
 

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Discussion Starter · #19 ·
How ironic-
I was thinking about going with Standard Motor Products [SMP] too.

I'm thinking about starting with the manual-tranmission mount first and save the motor-mount replacement for the spring/early-summer...
Cause to me, OE Toyota parts are way-over priced in general...

Anyway, How hard was it to replace the motor-mounts?

I've done GM mounts before on a trailblazer and they weren't any different in price than I remember.

Pain in the ass, but it was kind of my fault. The oil pan on the 2.4L isn't flat - so when you jack it up from the bottom the engine actually rotates as it goes up. Also, the location of a few of the bolts are a pain if you don't have an impact.

I would be interested to try it again but use an engine hoist and support it front the top.

To be honest, mine weren't as bad as I thought they were, and I got 100x the noise reduction from adding killmat 80mil sound deadening insulation to the floor and transmission tunnel.
 
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