AJP PR7 Problems: High Idle / Rough Running / Stalling / Not Starting (Idle Air Control Valve (IACV) Problems)

/ AJP PR7, Maintenance / Electricals / 10 minutes of reading

I’m writing this keeping AJP PR7 in mind, but it will be informative for any other bike owner, as well as some car owner’s, so – keep reading. Also, you probably have heard of people saying that you should never ever adjust idle screw on these for no reason, there is a good reason for that and i’ll explain why at a very bottom of the page, but first thing first – to find out what’s wrong with it (if anything), we need to know what the symptoms of the bad / clogged valve are, what this part is, what it is doing and how it’s functioning. 

And just to make sure: Idle Air Control Valve (IACV), Idle Air Control (IAC), Air Bypass Valve (ABV), Automatic Idle Speed (AIS) and Auxiliary Air Control (AAC) – are the very same thing.

Some use Stepper Motor to control the Valve, some Solenoid, and since AJP calls it “Idle Control Stepper Motor” in the parts manual – we already have a clue what’s inside of it.

That being said, let’s go step by step till we get to the end of this.

Table of Content:

What are the main symptoms of a bad, stuck or clogged IACV?

Engine not starting or starting and stalling straight away, stalls at stops (Stuck shut). High Idle (Stuck Open but it also can be Vacuum leak elsewhere thought).  Rough running or loss of power especially at higher altitude than normal / different temperature (Stuck somewhere midway).

Engine will keep running almost always if the throttle is opened manually, but If the engine stalls even with open throttle – problem is most likely elsewhere.

What Are the main Causes of a bad IACV?

  • Mechanical damage – especially on those with stepper motors, if something got stuck and the stepper motor forced the valve, there is a high chance that it broke the gears inside of it (Carbon deposits, misadjusted valves distance from the body – easily done if it was taken out for cleaning etc, more on that at the bottom). Also the unit can seize and break after so many hours of use too.
  • Electrical – burned out coils inside of the unit, damaged wiring loom.
  • It can be a software problem too, but to alter the settings there is a need to have proper tools to mess it up, and set values don’t just go and change themselves without someone’s input.
  • Another trouble but not quite at IACV’s fault – adjusted idle screw. This should never ever be touched or adjusted, but if someone adjusted to compensate for the broken IACV just to get the bike back home (or garage) it should be set exactly where it originally was after replacement of the unit, so – don’t play with it. Again – i’ll explain why at the very bottom of the page why!

What’s the purpose of the IACV?

It’s like an electronic idle screw that allows ECU to control the engine’s idle speed based on the readings it gets from the rest of the sensors (tps, o2, etc). Basically, ECU takes all the readings from all the sensors, and opens IACV or closes it in an attempt to keep idle at desired rpm for that specific engine. Desired rpm is set in the ecu’s software (and can not be changed without special tools) however how much it is opened at normal idle depends on a number of factors like temperature, altitude and how wide the throttle plates are open (TPS readings). 

So, in a very very short: It keeps idle smooth – no matter what.

What is an Idle Air Control Valve (IACV)?

In essence it’s a cone shaped valve fitted on the rod (called Pintle), moved by an actuator (stepper motor or solenoid magnet) that is controlled by ECU. 

Stepper motor is like any other dc motor, but instead of 2 wires it has 4, and 2 windings inside of it. It takes a bit more to control the stepper motor than a normal dc motor, but it can be controlled how far it goes very precisely if needed where the dc motor just spins. Name “stepper motor” – as it is controlled in tiny steps, 1 pair of wires – step 1, second pair of wires – step 2 (it’s a bit more complicated than that thought)… more steps stepper motor makes – a further in or out the pintle moves.

Where Solenoid type IACV is controlled by voltage, higher voltage the stronger magnetic field coils create – a further the pintle is pushed in (or out if in reverse). There is a lot more to it thought, but I hope the idea is clear.

Both types of valves will have some sort of channel within the throttle body that will allow air to bypass the throttle’s butterfly valves (throttle plates) with only one restriction – IACV. Further in the pintle is pushed into its seating area – the smaller the gap for air to pass between IACV and the channel walls – less air the engine gets, the lower the engine’s idle will be, and vice versa.

How does IACV interact with ECU on AJP PR7?

During the very first run (let’s say after ecu reset), ecu will “look” for the IACV setting where idle rpm is as close to desired rpm as it can be – that’s why PR7’s engine revs to 3k RPM and then slowly goes back down. The only way it can be done is by counting steps stepper motor makes to get to it. Ecu will memorize the number of steps it made, and it will use that number as a base line on the next startup. Problem is that there is no way for ECU to know where that valve physically is or how far it’s opened or closed, as IACV does not give a feedback to ECU and ECU has to count on the IACV to be exactly where it “ordered” it to be. Personally I do not like this part about IACV’s but more on that on my other post…

Where is the IACV / Idle Control Stepper Motor fitted on AJP PR7?

The IACV unit on the PR7 is fitted on the right top side of the throttle body. The stepper motor part is bolted on the outside, while the pintle sits inside of the bypass channel withing the throttle body. 

How to check if PR7’a idle control valve is actually working. 

Well… there is no easy way to make sure it’s actually at 100%, and more often than not -it’s either working or not working at all. Here are a few steps on how to check it…

  • Literally just listening after the engine was stopped. After ignition is switched off, IACV is normally parked in its resting position and without engine noise there will be a noticeable “clunk” within the throttle body. This would be a good indication that IACV is actually functioning (doesn’t mean it’s working properly thought).
  • Electrical part can be checked without taking anything apart, only by removing the plug from the ECU (battery should be disconnected first thought!) and checking the resistance between the wires leading to the stepper motor. Pre 2021 PR7 is using: red/blue, orange/black, green/black and yellow/red wires to control IACV.  And since there are 2 coils, 2 pairs should give the same (or very similar) resistance reading with a multimeter, and nothing else (if it does, something is shorting within the unit). Problem is that only the electrical part of the IACV is checked that way. 

Manual States: Solenoid resistance should be – 53Ω±10% 

What I have personally measured on my PR7’s ECU Grey plug is : Pair 1 – Green/Black and Yellow/Red 50.2 ohm, Red/Blue and Orange/Black 49.5 ohm. 

(if OL (off-limit) then IACV and wiring should be checked separately).

  • Checking PR7’s idle control valve’s movement “by eye”, means literally having a peak at the valve to see if it’s closing and opening when the throttle is moved. Obviously that involves a bit more of dismantling and I really would not suggest this method, as a lot of bad things can happen, but if there is no choice, than… filter box off, and while trying to start the bike looking inside of the bypass channel to the valve itself- valve should move right to left (if it’s functioning at all) with increased rpm by turning the throttle grip… like I mentioned before – would not suggest practicing this method, as running an engine with no filter on, means all the dust will be sucked in…
  • Even if IACV is mechanically sound and coils are intact, there still might be wiring that’s damaged between IACV and ECU, lucky for us PR7 owners there are only 4 wires to check for continuity (Green/Black; Yellow/Red; Red/Blue; Orange/Black;),
  • And finally, even if everything is fine, there still might be a problem with the ECU itself, and an OBD reader and a special software is needed to check / adjust that…

Big Thank You to Paulo N. for this very important pointer!

Very important note: if the IACV valve was removed for cleaning / lubricating or any other reason, it is very important to make sure that it is recalibrated before inserting it back! 

And now the fun part.

Why you should never adjust the Idle Control Screw on throttle bodies with Idle Air Control Valve (IACV)?

Ok, so unless you really want to get rid of the IACV despite its usefulness for keeping smooth idle, you should not play with that screw. Here is why: Imagine you have two kids on the seesaw, one is called IACV, the other TPS. Both weigh the same unless we turn the idle control screw that will push TPS towards the center of the seesaw. ECU is the pivot point under the seesaw that moves towards one or the other of the kids to keep the seesaw perfectly balanced ( at Desired Idle RPM). ECU is happy to shift back and forth as it has plenty of room to move around if some other factors comes in to play like not so dense air like at higher altitudes, temperature changes – again dense or not so dense air, but if we adjust the idle screw and open up the butterfly valve we suddenly make TPS – a fat kid that sits very close to the center of the seesaw. Ecu – not happy, as it will have to shift towards the IACV to keep things at balance (Close IACV down to compensate for open throttle’s butterfly valve). More we turn the idle screw – the harder it gets for ecu to balance it. Sooner or later ECU will run out of room for adjustments, and one of the ends of the seesaw will come down crashing (Crashing = troubles starting at cold / hot, problems with idle at different altitudes) and ECU will no longer be able to balance it out, unless that idle screw is turned back where it was – giving back ECU all the controls it needs. 

In other words, when the throttle is opened – IACV valve gets closed, and by opening the throttle with an idle screw, we only give a reason for ECU to close the IACV valve as it will try to bring RPM back down to the set Desired rpm range, and more throttle is open less control ECU has and less likely ECU will keep engine running smoothly when different factors will come into play – kind of useless if you think about it.

Final note

It might sound a bit complicated and dull, but in reality it isn’t once you get the idea (and I hope this post gave a good idea about it). Thing is, IACV’s are not serviceable as they are sealed units, they can be cleaned a bit and lubricated to push their limit slightly, but if it breaks, it breaks and it has to be replaced. Also, there is no real reason for taking it off and cleaning it once in a while unless it’s causing troubles, but if it doesn’t – don’t fix what’s not broken and leave it alone.

Explore more!

All AJP PR7 MODS:

OR

AJP PR7 Faults, Fails and Fixes

Explore More!

A list of posts about Bike Maintenance and General Modifications that might be Interesting to know! 

General Modifications:

  1. Throttle Tamer Mods (4 ways to tame your horse!)
  2. Projector headlight conversion from right side road traffic to left and vice versa. 
  3. How to make your own Exhaust or how to modify an existing one.
  4. Power Commander (PCV) and Thoughts on it.
  5. Brake Snake / Pedal Anchor – why and how!
  6. Lighter Clutch Mods:
  7. Rear Suspension and Drive-Train:
  8. The List of Most Useless Adventure Motorcycle Mods And Bling!
  9. Dangers of the lowering kits (things to know before Lowering your Bike!

Bike Maintenance:

  1. How to pass MOT the first time – every time!
  2. How to Maintain your motorcycle Locks (works with all locks!)
  3. Best Suspension Bearing Grease!
  4. What grease to use on your motorcycle?
  5. How to shorten Life of your wheel bearings! (Or what not to do to them!)
  6. Why should you grease your bolts! (And not only Bearings!)
  7. What is the best Chain Lube for your motorcycle?
  8. How to buy used Motorcycle – Free Guide.
Recommend this article on:

Related Posts

Scroll to Top