Low Idle

[BLACK'98DSM]

I'm thinking it's because I need a tune, but let's hear your input.

- Car idles at 750-850 rpms once warm.
- Idle is a little rough (not bad, but noticeable)

It's cammed, but only a mild exhaust cam shouldn't effect it this much, right?

 

[techboy]

There's a difference between a rough idle and a low idle. Your idle rpm is the recommended idle speed from Mitsu, so I don't think its low.

Was it rough before you installed the cam? I'd bet the slight roughness you feel is related to the can or a slight vacuum leak. That's about the only other thing that would cause a rough idle.

 

[BLACK'98DSM]

or a slight vacuum leak

I thought the rpm would be raised due to a vacuum leak?

Was it rough before you installed the cam?

No, but it had a high idle so I can't vouch for how it would have been.

 

[techboy]

Often a vacuum leak will make it high, but I've also seen a rough idle in a DSM due to vacuum leak as the car tries to compensate for it. Now that you said it was high before the cam it makes me wonder even more. Often times it's the TB gasket.

 

[95_gsx_2g]

Just out of curiosity do you got any tuning software or is it just on a stock ecu? Aftermarket cams like my gsc 274s like to lope alot and sound alot more choppy compared to the stock cams which I absolutely love! I actually prefer a target idle of 950-1000ish idle in my dsm. It just drives better that way with all the mods and being a manual. Check good for boost leaks, bad isc, biss etc.

 

[ThunderChild]

OP has a 420a just to be clear. I agree it sounds like it may be a vacuum leak. If the leak is small enough the car will try to compensate and it may cause a rough idle, especially with cams.

What cam(s) do you have?

Have you verified you don't have a fuel/spark problem?
And have you verified mechanical timing is in spec?

A video of the rough idle may help as well, could all just be a result of the cam lope.

 

[BLACK'98DSM]

A video of the rough idle may help as well, could all just be a result of the cam lope.

The idle can be felt but not really seen. I thought since I only upgraded the exhaust cam it wounldnt have the typical cammed rumble effect. But maybe I was wrong.

What cam(s) do you have?

233 exhaust and stock replacement intake. They both came in a kit from carid.com a while back.

is it just on a stock ecu?

For now I'm on stock ecu. I really badly want a Megasquirt, that is somewhere down the list of future mods.

 

[BLACK'98DSM]

Your idle rpm is the recommended idle speed from Mitsu

Good. Whatever then