intake manifold carbon buildup cleaning, for 1996-1999 mk3 VW Jetta or Passat TDI
DIY removal and cleaning of intake manifold of carbon build up, for 1996-1999 Volkswagen Jetta or Passat TDI
The intake manifold must be regularly cleaned of carbon buildup. This DIY shows how to remove the soot buildup from your TDI engine.
There is no factory replacement interval, it should just be cleaned when there is significant buildup. This carbon buildup can reduce performance and efficiency. Now that all diesel fuel sold in North America (not Mexico) is ultra low sulfur diesel (ULSD) only, clogging problems should be much less. Unlike the mk4 cars, the egr is part of the intake manifold and cannot be removed separately. Because of this, I suggest cleaning it and reusing it instead of buying a new one since a new manifold is over $500. Otherwise you have to use a pressure washer and/or brush to scrub it clean. Wear old clothes because they will be stained after you clean the intake manifold. Always wear gloves and eye protection when cleaning the manifold. The carbon is very sticky and a pressure washer or brush alone can't reach the interior corners.
I do not recommend bead blasting since improper cleaning can leave tiny particles stuck in the carbon and cause engine damage. There are chemical cleaners that work while the manifold is attached to the engine but I strongly do not recommend this. Dealers used to do this until engines were damaged. In a diesel, the valves are almost touching the pistons due to high compression and once you see how much crud is inside, you won't want that going through the engine with the cleaner You also don't want the gunk to go through the turbo. If the cylinder head is really bad you should remove the head for cleaning.
Soaking the manifold in carb cleaner, biodiesel, or wood furniture stripper will clean the carbon effectively.
I suggest buying new allen bolts ahead of time because by now they're probably rusty and seized. If you do get stripped bolts, use a deep socket bolt-out tool. The shallow socket bolt out tool won't reach.
This is a good time to also clean the EGR cooler. This is the round cylinder that leads to the EGR. Removing the EGR cooler causes a little coolant to be spilled so have replacement coolant available. Warning: check the color of your coolant, do NOT mix green/blue coolant with VW red/purple coolant, refer the article: 1000q: coolant flush for more details.
Some people put a EGR block off plate because this will greatly reduce any intake buildup in the future. Disabling or reducing the EGR cycling will increase emissions and could cause a check engine light to appear. For more EGR information, see 1000q: TDI EGR system FAQ.
Note: if you have a 1996 passat TDI, you do not have an EGR cooler. All other models do, differences are noted below in the procedure section.
Parts (click links to compare current prices)
6mm ball end allen wrench or socket, straight end allen wrench is preferred since it will help avoid stripped allen bolts
mirror to see the back of the engine
a brush, degreaser, and a power washer, biodiesel, or other solvent
6x 6mm allen bolts for the intake manifold (size: m8x45, also used on ALH engine) (optional but suggested) VW# N-904-242-01
egr gaskets VW# 069-131-547-D (can be reusable)
intake manifold gasket VW # 028-129-717-D or from idparts (manual suggests replace ev time)
NOTE-some intake manifolds do not have the EGR cooler, part number ending in "J" should have the EGR cooler, ending in "T" should not have one. Make sure to double check the part numbers with your vendor! It looks like "J" has bolt holes for the cooler but some vendors list "T" for both parts. Later mk4 ALH manifolds will not bolt on, especially since the manifold points to the the other side.
With EGR cooler - VW # 028-129-711-J
Without EGR cooler VW # 028-129-711-T if you have a 1996 passat and do not have an EGR cooler.
VW G12 coolant (not needed on 1996 passat). Do not use green coolant or other type coolant, see 1000q: coolant flush for more details.
hose clamp pliers (optional but suggested) Bolt-out tool for stripped allen bolts (optional, don't get the low clearance set)
Intake manifold cleaning procedure
Remove the top engine cover. 3x 10mm nuts.
Remove turbo outlet piping and intercooler-manifold piping by removing their hose clamps and any vacuum lines. Tape over the exposed pipes so nothing falls in. I prefer tape over paper towels because paper towels tend to get stuffed into the pipe and forgotten.
If you have a 1996 passat, your car looks like this: It's pretty much the same but you have no EGR cooler, intake removal will be even faster!
Optional: You can remove the accordion hose/turbo intake hard pipe for easier access but I don't suggest it. There is an o-ring seal at the turbo intake and it's best not to disturb it. Circled below are the 3x 10mm bolts holding the pipe. You should also remove the crankcase vent (CCV) oil line heater (the electrical plug) When you put the piping back, lube the o-ring before putting it back and twist/wiggle it on to avoid pinching the o-ring. If you need a new turbocharger flange o-ring, the part number is #1h0 129 646.
Remove the EGR-EGR cooler metal piping (2x 6mm allen bolts per flange). NOTE: if you have a 1996 passat, you have no EGR cooler, skip this step. Make sure to catch the gaskets so they can be reused. Remove the EGR cooler water hoses. There are 3 hoses. Then remove the EGR cooler (3x 10mm bolts)
Unbolt 3 bolts holding the EGR cooler down (red circles in below pic). Use a mirror to positively identify them. Disconnect EGR cooler intake and outlet hoses. Remove EGR cooler intake and outlet flanges (2x 6mm allen each flange), some PB blaster works great here. It may be hard to get access to the nuts on the exhaust manifold so you can leave that section in place. The EGR cooler can now be removed.
To finish disconnecting the intake manifold remove the rest of the bolts (6x 6mm allen bolts, 1 hole is circled in red). It's hard to get a good picture, so here is the manifold after removal. Note - you may want to use PB Blaster to soak and pre-lubricate the bolts. You may also want to buy 6 new bolts in case they are damaged or get stripped during removal. The 3 bright areas in the below pic is the EGR cooler bolt location. The 1996 passat intake manifold has flat machined pieces with no bolt holes since it has no EGR cooler.
Some people choose to remove or block off the EGR cooler and EGR system. On the mk3 TDI, it's part of the intake manifold and is not easily removed so you can block off the coolant and EGR tube instead. Refer to 1000q: EGR FAQ for more details about EGR blocking, the purpose of the EGR, etc.
The EGR naturally puts exhaust soot into the intake which must be cleaned out. It mixes with oily crankcase vapors and can form a buildup. Do NOT use a chemical dissolver or a vacuum cleaner to suck out the carbon while the intake manifold is still attached to the head. Hard pieces of carbon will fall into the engine and could damage the valves or turbo. The intake, EGR, and EGR cooler must be removed from the head for cleaning.
The cylinder head is best cleaned while off the car. If you want to clean the cylinder head while on the engine, I suggest removing the camshaft (follow timing belt removal as spec. in your factory service manual or see 1000q: timing belt removal so that all the valves are closed, or rotate the camshaft so that the valves on the cylinder you are cleaning are closed. You can then use a brush to clean. I would avoid using liquid cleaners in case it were to leak into the engine and cause hydrolock (engine damage). Make sure to follow up with compressed air to blow out all loose carbon particles. I've also heard of filling the manifold with carb cleaner, old nuts, and shaking it or to use an old hacksaw blade to get to the corners (hacksaw tip by P2B).
Below are some pictures showing a moderately dirty intake. It looks worse than it really was because of the curve in the manifold neck. The worst buildup tends to be downstream of the EGR.
Pictured below left is the manifold near the intake ports, there was only a moderate/light coating of carbon so removing the cylinder head was unnecessary. Note the oil stain below the EGR vent hole. After cleaning, the hole was tapped and a drilled out fitting/hose was screwed in to divert the oil leak, pictured bottom right.
You have to look on the downstream side of the EGR to see the really bad clogging.
Buying a new manifold will let you immediately change it and save car down time but they are more expensive on the mk3 TDI because the EGR is part of the manifold. A new manifold should avoid the EGR weeping issue but I chose to clean the old manifold. I used a pressure washer, soaked it in carb cleaner w/brushing, and used the pressure washer again. Soaking the manifold in carb cleaner, biodiesel, or wood furniture stripper will clean the carbon effectively.
A hose will not clean it, you need a pressure washer like the one at the carwash! It will cause a big mess, so wear clothes you don't mind getting stained. Make sure to look inside the manifold as well, the corners and neck hide a lot of carbon. Other options for cleaning involve ultrasonic cleaning or soaking in biodiesel.
I have a junk table and clamps to prevent the manifold from blowing away. A carwash type electric pressure washer will also work but these aren't as powerful because they would otherwise damage cars. The pictured manifold is from another engine, your mk3 manifold will look similar.
Installation is the reverse of removal. The service manual says that the intake manifold gasket is one use only but you can reuse the old gaskets if they are not damaged. The intake manifold gasket's beading (coating) faces the intake manifold.
Torque specs: 6mm intake manifold allen bolts - 18 ft lbs.