Rough idle and dies, TPS fine, valves good

[schmalexthefryer]

Hi all,
My bike idles poorly and jumps around in rpm from 900-1250, but the moment I roll on the throttle it behaves beautifully.

I have no idea what’s causing this so I first checked the valves. The intake is shimmed pretty tightly to 0.09mm and the exhaust to 0.25mm. This didn’t fix the issue so I then checked the TPS. It’s currently reading 0.6 without touching the throttle so that seems fine.
I then adjusted the idle screw to see if adding a little more idle speed would help and no change.

as it stands the bike currently idles poorly and dies almost every 30 seconds at red lights, but when on throttle seems healthy through the entire rev range.

does anyone know what could be causing this issue? It seemed to start rather suddenly, I just went for a long trip on the bike and didn’t notice the issue until riding around town for a week or so after the trek

 

[SPORTY9]

Does it still have the charcoal canister?

 

[schmalexthefryer]

Does it still have the charcoal canister?

Yep, should I disconnect lines or something to it? I’ve literally never messed with it

 

[DaveySprocket]

An intake manifold leak can cause erratic idle. Warm up the engine, try to get it to idle. Maybe have an assistant hold the throttle steady at as low of an RPM as possible. spray some carb clean around the intake manifold seal areas. If you have any change in idle, either higher or lower/stalls) then you have an intake manifold air leak.

 

[SPORTY9]

Yep, should I disconnect lines or something to it? I’ve literally never messed with it

You could have raw fuel in the charcoal canister. It happened on my Interceptor and it had the same symptoms as your bike. You can disconnect and recheck. Also DaveySprocket is correct about an intake leak causing erratic idle. Both are easy to check. Let us know what you find out.

 

[tom_d]

Check your spark plug wire boot to wire connection on both ends and make sure it is tightly screwed all the way on.

 

[OldGuy]

You didn't say what year - carb or EFI?

 

[Roy Gavin]

A tank of bad gas can give the same symptoms- I had a carbed Honda VFR which did the same thing if I just filled up at the wrong station.
When the tank is off at service time I tip and flush , current fuel doesn't take long to go off.

 

[schmalexthefryer]

You could have raw fuel in the charcoal canister. It happened on my Interceptor and it had the same symptoms as your bike. You can disconnect and recheck. Also DaveySprocket is correct about an intake leak causing erratic idle. Both are easy to check. Let us know what you find out.

I went ahead and unplugged the

Hi all,
My bike idles poorly and jumps around in rpm from 900-1250, but the moment I roll on the throttle it behaves beautifully.

I have no idea what’s causing this so I first checked the valves. The intake is shimmed pretty tightly to 0.09mm and the exhaust to 0.25mm. This didn’t fix the issue so I then checked the TPS. It’s currently reading 0.6 without touching the throttle so that seems fine.
I then adjusted the idle screw to see if adding a little more idle speed would help and no change.

as it stands the bike currently idles poorly and dies almost every 30 seconds at red lights, but when on throttle seems healthy through the entire rev range.

does anyone know what could be causing this issue? It seemed to start rather suddenly, I just went for a long trip on the bike and didn’t notice the issue until riding around town for a week or so after the trek

I did an EVAP delete and had no improvements which leads me to think it’s an intake leak of some kind. I’ll check this out now.

this leads me with another question, when I did the charcoal canister delete, lots of people are saying to plug the line from the throttle body to the charcoal canister. It made no difference either way to how the bike performed when I tried running it plugged and unplugged.
Why would people recommend plugging it, is this not the same as a blocked up charcoal canister if you leave it plugged?

 

[schmalexthefryer]

Hi all,
My bike idles poorly and jumps around in rpm from 900-1250, but the moment I roll on the throttle it behaves beautifully.

I have no idea what’s causing this so I first checked the valves. The intake is shimmed pretty tightly to 0.09mm and the exhaust to 0.25mm. This didn’t fix the issue so I then checked the TPS. It’s currently reading 0.6 without touching the throttle so that seems fine.
I then adjusted the idle screw to see if adding a little more idle speed would help and no change.

as it stands the bike currently idles poorly and dies almost every 30 seconds at red lights, but when on throttle seems healthy through the entire rev range.

does anyone know what could be causing this issue? It seemed to start rather suddenly, I just went for a long trip on the bike and didn’t notice the issue until riding around town for a week or so after the trek

Also, the bike is EFI

 

[DaveySprocket]

I went ahead and unplugged the

I did an EVAP delete and had no improvements which leads me to think it’s an intake leak of some kind. I’ll check this out now.

this leads me with another question, when I did the charcoal canister delete, lots of people are saying to plug the line from the throttle body to the charcoal canister. It made no difference either way to how the bike performed when I tried running it plugged and unplugged.
Why would people recommend plugging it, is this not the same as a blocked up charcoal canister if you leave it plugged?

The nipple on the throttle body would suck unfiltered air into the engine if it were not capped off.

 

[schmalexthefryer]

Hi all,
My bike idles poorly and jumps around in rpm from 900-1250, but the moment I roll on the throttle it behaves beautifully.

I have no idea what’s causing this so I first checked the valves. The intake is shimmed pretty tightly to 0.09mm and the exhaust to 0.25mm. This didn’t fix the issue so I then checked the TPS. It’s currently reading 0.6 without touching the throttle so that seems fine.
I then adjusted the idle screw to see if adding a little more idle speed would help and no change.

as it stands the bike currently idles poorly and dies almost every 30 seconds at red lights, but when on throttle seems healthy through the entire rev range.

does anyone know what could be causing this issue? It seemed to start rather suddenly, I just went for a long trip on the bike and didn’t notice the issue until riding around town for a week or so after the trek

hi all, an update on the bike
I’ve taken out the charcoal box, no improvements,
I adjusted the valves, TPS and idle screw, no improvements.
I just shot some carb cleaner around the intake and didn’t see a change in rpm.

the bike still drives good but it can’t idle without me holding the throttle open a bit. I’m really at a loss for what it could be.

is it possible my cam is a little worn out? Bike is 8k miles so seems unlikely. What about other sensors? MAP or exhaust? The bike has an aftermarket exhaust.

 

[schmalexthefryer]

You could have raw fuel in the charcoal canister. It happened on my Interceptor and it had the same symptoms as your bike. You can disconnect and recheck. Also DaveySprocket is correct about an intake leak causing erratic idle. Both are easy to check. Let us know what you find out.

Hey, I checked the charcoal and saw no improvement, and wasn’t able to effect the idle by spraying carb cleaner around the intake

 

[Hairy Potter]

Have you swapped the spark plug to check that?

 

[Laserman]

Does this bad idle happen when cold? Between Cold/Hot? When Full Hot? All the time? Do you ever get pinging at high-load with less than full throttle?

I ask because from 2K miles onward mine developed an idle problem when cold, which then expanded to persist until it reached operating temp. Once there, it was fine. I installed DNA intake and Booster Plug and didn't have a problem again unless my valves start getting tight. I get lean pings with big headwinds at >80F tho.

If this issue is constant, I suspect your engine is just running too lean. Our US-spec are lean af new and it just gets worse with intake and exhaust mods. BP aint enough.