Tech tip: Intake valve deposits cause rough engine
Thread Starter
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Tech tip: Intake valve deposits cause rough engine
Something we often forget when we're chasing odd driveability issues is to check for intake valve deposits. Back when I had a carb I had an intake manifold that leaked on the bottom, sucking oil into the ports. It wasn't horrible, about 1 quart every 800 miles. Not enough to foul the plugs, even.
Then I swapped to EFI and when the intake was off I noticed quite a bit of sludge on the valves.
I wasn't too happy with the way the engine ran. Symptoms were:
Off idle hesitation
Part throttle, low rpm "miss"
Rough idle.
Hard start.
Turned out all this was caused by those pesky intake valve deposits. I poured several cups of water into the engine, and then ran deposit remover in 3 tanks of gas.
The difference is amazing. It now idles smooth, throttle response is great, starts better and is just smoother and more powerful.
I noticed several forum members have had intake sealing issues, so after you get it fixed it is a good idea to run some deposit remover in the tank.
I used prestone concentrate which worked great, but I'm sure there are other good products out there.
Then I swapped to EFI and when the intake was off I noticed quite a bit of sludge on the valves.
I wasn't too happy with the way the engine ran. Symptoms were:
Off idle hesitation
Part throttle, low rpm "miss"
Rough idle.
Hard start.
Turned out all this was caused by those pesky intake valve deposits. I poured several cups of water into the engine, and then ran deposit remover in 3 tanks of gas.
The difference is amazing. It now idles smooth, throttle response is great, starts better and is just smoother and more powerful.
I noticed several forum members have had intake sealing issues, so after you get it fixed it is a good idea to run some deposit remover in the tank.
I used prestone concentrate which worked great, but I'm sure there are other good products out there.
Safety Car
Joined: Feb 1999
Posts: 3,631
Likes: 14
From: Fountain Hills AZ
Re: Tech tip: Intake valve deposits cause rough engine (zwede)
Good advice Zwede. I've also seen sludge on engines with rich idle mixtures, especially on those that see a lot of idling in relation miles driven. While the detergent package in most gasolines do a good job of keeping the backs of the valves clean in efi cars, they don't always keep up with the amount of buildup often seen in carbed engines, especially those with big cams and carbs.
Thread Starter
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Re: Tech tip: Intake valve deposits cause rough engine (virtue4u)
I use 2 cups, each holds 12 oz. I rev the engine to 2000 rpm and pour in as fast as possible without stalling the engine. After the last of the water is gone, I rev it a little higher for a few seconds until it smooths out before letting it idle.
I wouldn't do it more than once a day for 2-3 days. Some of the water goes past the rings into the oil. After driving for 10 miles or so, it will boil out of the oil.
The first time I did this, there was a big cloud of blue/black smoke out the tailpipes. The third time there was very little smoke. I figure the amount of smoke depends on how much crap is in the engine.
The water trick will also clean intake ports, combustion chambers and spark plugs. Unfortunately it does very little for the exhaust valves.
I wouldn't do it more than once a day for 2-3 days. Some of the water goes past the rings into the oil. After driving for 10 miles or so, it will boil out of the oil.
The first time I did this, there was a big cloud of blue/black smoke out the tailpipes. The third time there was very little smoke. I figure the amount of smoke depends on how much crap is in the engine.
The water trick will also clean intake ports, combustion chambers and spark plugs. Unfortunately it does very little for the exhaust valves.
Race Director
Joined: Dec 2000
Posts: 10,896
Likes: 2
From: CO
Re: Tech tip: Intake valve deposits cause rough engine (zwede)
Im a newbie to all this and pouring water in my engine sounds awful. :confused:
But hey, if you guys say it works. Which to use? tap water or distilled? :jester
But hey, if you guys say it works. Which to use? tap water or distilled? :jester
Race Director
Joined: Jul 2002
Posts: 13,858
Likes: 0
From: A 12/8 man in a 4/4 world
Re: Tech tip: Intake valve deposits cause rough engine (zwede)
my daily driver (96 lumina sedan) has this kind of problem. this solution should work here also? think it would be tough to get past all the intake sensors. btw, would water hurt them?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Le Mans Master
Joined: May 1999
Posts: 6,692
Likes: 29
From: Texas
Re: Tech tip: Intake valve deposits cause rough engine (zwede)
Let me jump in with a question or comment.
I have seen repair shops use the intake, upper cylinder cleaner that is sucked slowly out of the bottle by a small hose attached to in intake vacuum, such as the PCV valve, or the brake booster vacuum.
Does it make sense to slowly introduce the H2O into either of those?
I have seen repair shops use the intake, upper cylinder cleaner that is sucked slowly out of the bottle by a small hose attached to in intake vacuum, such as the PCV valve, or the brake booster vacuum.
Does it make sense to slowly introduce the H2O into either of those?
Melting Slicks
Joined: Dec 2000
Posts: 2,198
Likes: 2
From: Eastern Connecticut
Re: Tech tip: Intake valve deposits cause rough engine (Larry82)
Water down the carb is an old trick - it basicly steam cleans the upper end of the motor. You have to pour it rather quickly, but not so fast it stalls. It isn't necessary to over engineer this. (as fun as that can be ;) Joe
Thread Starter
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Re: Tech tip: Intake valve deposits cause rough engine (Larry82)
I don't think it would be possible to do the water trick on an engine with a forward facing throttle body. For those, you'd be better off with some cleaner that goes in through the PCV hose.
Also, first thing to try is just some detergent that goes in the gas. Unless you have really bad buildup, that should take care of it.
Also, first thing to try is just some detergent that goes in the gas. Unless you have really bad buildup, that should take care of it.
Race Director
Joined: Jul 2002
Posts: 13,858
Likes: 0
From: A 12/8 man in a 4/4 world
Re: Tech tip: Intake valve deposits cause rough engine (zwede)
been using carb/injector cleaner often in the gass. helps. but still problematic. thought about using spray bottle to spray thru the intake... pcv is a great idea.
Safety Car
Joined: Feb 2002
Posts: 4,286
Likes: 4
From: Guam
Re: Tech tip: Intake valve deposits cause rough engine (Got79Fever)
I remember when I was a kid back in the early seventies. I used to buy used cars and resell them in order to save enough money for college. I could not afford to spend a lot of money on tune ups. So if a car was running rough, I would first try pouring water in to the carb. If that did not work, I would pull the plugs, dist cap and rotor and clean and polish the contact surfaces. The water method worked 9 out of 10 times.
My method was to fill two small coke bottles with water. Run the car at a fast idle and slowly pour the water in. Be careful not to pour too much water. You don't want to hydra lock the engine and bend a valve. If that did not work too well, I would cool the engine first then I would restart the engine and pour a half a bottle of ATF first, then pour the two bottles of water. The ATF is like a soap and loosens the deposits.
I don't do that anymore as there are better ways to do things. But boy does that story bring back memories.
:cool: :cool:
I forgot to add that you should only do this to gas engines. Diesel engines can be damaged by doing this.
[Modified by Sharky Guam, 10:09 AM 7/23/2002]
My method was to fill two small coke bottles with water. Run the car at a fast idle and slowly pour the water in. Be careful not to pour too much water. You don't want to hydra lock the engine and bend a valve. If that did not work too well, I would cool the engine first then I would restart the engine and pour a half a bottle of ATF first, then pour the two bottles of water. The ATF is like a soap and loosens the deposits.
I don't do that anymore as there are better ways to do things. But boy does that story bring back memories.
:cool: :cool:
I forgot to add that you should only do this to gas engines. Diesel engines can be damaged by doing this.
[Modified by Sharky Guam, 10:09 AM 7/23/2002]
