Hot air intake valve problem

[Hilux Hetti]

Hi all.

Some time ago I posted that I was having problems with drive-ability of my 97 carby aspirated 2.4lt Hilux DX. When I used it on very cold mornings, it would run alright for 4 klm, then start jerking violently as in the carb icing up. If I put the foot down hard to bring in the second throat, it would pick up immediately and go hard until I had to back off, then the "pig-rooting" would begin again. Throw the clutch and it would stall necessitating the old "heel and toe" routine on the throttle and brakes. Very dangerous if heavy traffic. Since that post, the warmer weather arrived and all's been well until recently..........

With the arrival of frosty weather and 2 degree temps in the morning, the same problem has emerged. Definitely carby icing, so I by-passed the HAI valve (Hot Air Intake) and it seems to have cured the problem. The now constant vacuum is keeping the flap in the air horn of the intake shut thereby causing the intake to pull warm air from the exhaust manifold. Not good for proper fuel mix, but it works. God knows what it will do to my already horrific fuel (non) economy of 16mpg!

The questions I wish to ask you knowledgeable people is........ Can this valve loose it's properties thereby causing it to open too early? Do these valves become faulty with age? (My 1990 Seca also has one and it continues to work perfectly) Or, is it a common fault with these vehicles?

Any help greatly appreciated as I've decided to sell the vehicle to a friend and I don't want it causing him grief.
Thanks already,
Hilux Hetti.

[Hilux Hetti]

Hi all.

Some time ago I posted that I was having problems with drive-ability of my 97 carby aspirated 2.4lt Hilux DX. When I used it on very cold mornings, it would run alright for 4 klm, then start jerking violently as in the carb icing up. If I put the foot down hard to bring in the second throat, it would pick up immediately and go hard until I had to back off, then the "pig-rooting" would begin again. Throw the clutch and it would stall necessitating the old "heel and toe" routine on the throttle and brakes. Very dangerous if heavy traffic. Since that post, the warmer weather arrived and all's been well until recently..........

With the arrival of frosty weather and 2 degree temps in the morning, the same problem has emerged. Definitely carby icing, so I by-passed the HAI valve (Hot Air Intake) and it seems to have cured the problem. The now constant vacuum is keeping the flap in the air horn of the intake shut thereby causing the intake to pull warm air from the exhaust manifold. Not good for proper fuel mix, but it works. God knows what it will do to my already horrific fuel (non) economy of 16mpg!

The questions I wish to ask you knowledgeable people is........ Can this valve loose it's properties thereby causing it to open too early? Do these valves become faulty with age? (My 1990 Seca also has one and it continues to work perfectly) Or, is it a common fault with these vehicles?

Any help greatly appreciated as I've decided to sell the vehicle to a friend and I don't want it causing him grief.
Thanks already,
Hilux Hetti.

Since none of you seemed able to offer an opinion on the above matter, I did some extensive research myself and actually found a mechanic and one other person who both owned similar vehicles and had exactly the same problem with icing up of the carby on a mid 90ies Hilux ute on cold mornings. Apparently, it IS a production fault common to those Hilux models and can be cured by taking the hot air intake valve out of it's position in the air cleaner element body and moving it to a more suitable position. You can also get around it by doing what I did and making sure the cold air flap towards the front of the engine stays shut during cold weather. The latter is a case of "two wrongs making a right" but it works, although if you don't set it back to factory specs during warm weather, it may ping on hills or under load.