Piston Slap: …but the Kitchen Sink

Sajeev Mehta
by Sajeev Mehta
piston slap but the kitchen sink

Will writes:

Hi Sajeev, I am heeding your call for more questions.

1) Can a crack around one of the intake system tubes (thanks, shopmonkeys!) to the right of the Throttle-Body on an ’01 MkIV Jetta GLS 2.0 be the source of a lumpy idle (+even decreased mileage)? -I think it’s the Y-Tube next to the PCV. (also: last time I checked, this pipe was something like $200 to replace new from the stealership)

2) How necessary is it to ‘Bed-In’ new brake pads on new rotors? (ala StopTech’s instructions) Reason being, I just [made the mistake of] put[ing] Mintex Red Boxes on with new rotors, but no bedding, and seemed to get wobbly cementite deposits within 1 month! (note: since then, have just switched over to mild-upgrade slotted rotors and stock ATE pads as an avoidance maneuver)

3) Is the Cabin Light switch easily+cheaply replaceable on that Jetta? It seems to have gone on the Driver’s door.

4) I have Kumho Ecstas on this car that show a higher PSI range. I think max is like 51PSI or something. If the standard spec is like 28/26 with Stock Michelins, then how much higher should I run the Kumho’s? -36PSI on all 4 corners?

5) Should I rinse/wash the car LESS frequently in the winter to reduce potential corrosion if I live in an area that gets lots of road-salt in the winters?

6) I had to replace my Front Rotors. -Will I Ever have to replace the rears? -Is their wear-rate like less than 1/2 of the Fronts?

7) When would an ’01 Jetta in the Greater-NYC area start rusting-out? -I had a MkII that kinda started falling apart, -nearly Fred Flintstonte-style.

8) In that same geographical suburban area (not IN NYC), how much -years/% does parking a car Outside shorten it’s useful life vs. Garaged? -In general? -By other US geographical regions?

9) Similarly, if I have a used car I want to get in the future that might be fragile, where should I get it from? -Arizona? SoCal? Nevada?

10) Does a Throttle Body or MAF ever really need to be cleaned? -Or are the forums guys just being really obsessive? -Aren’t MAFs EXTREMELY finicky and fragile to clean?

11) What other intake/induction system parts or valves/membranes should be given a solvent rinse, if you were to pull the thing apart? PCV? All the tubes? What solvent(s) to use?

12) Are there weird Throttle-Position-Resetting-Routines that have to be gone through if you Do pull the TB to clean it? -Would it screw up the ECU if you didn’t? Do I need a special Code-clearer like a VAG-COM+Laptop to do this?

13) If I re-do the shoes on Rear Drum Brakes, can I just slap the damn new ones on, or do I really have to shoot everything down into a catch-pan with that brain-destroying Brake Parts Cleaner Spray first? -Swear to God, even with a respirator on, and outdoors, the first(+last) time I used that s***, I got a mad, pranging headache.

Sajeev answers:

Let’s see if I can nail all of these via shooting from the hip. Quick draw and rapid fire: Best and Brightest, do your worst. It’s on…SON!

1. Yes, that’s a classic problem stemming from a vacuum leak. Which you probably have from what I read there.

2. I have no clue. That said, always break in new pads/rotors to ensure you don’t wind up with the problem you mentioned. While it might not be necessary on every car/pad/rotor, it’s just the right thing to do.

3. That’s a question for the forums, but since this is a MK IV Jetta, I guess this is neither cheap nor easy to replace. Considering the rest of the car, there’s a good chance I’m right.

4. Never base your tire pressure on the number listed on the tire’s sidewall. That’s the max pressure and has zero correlation with what’s ideal for your car. Most vehicles need 28-35 psi at each corner, but read your owner’s manual to know the truth.*

5. Yes. I never verified it (Houstonian, ‘natch) but the concept of pouring water in every drain hole and letting it freeze shut sounds like a great idea to me. Time consuming and pretty insane, but the theory that salty water can’t get in when all the holes are frozen shut really speaks to me. Oh, and never park in a heated garage for this reason. Park outside when its salty out there.

6. I’ve heard the wear rate is usually more like 80/20, unless you do a lot of towing.

7. Too many variables to make such a blanket statement. That said, when it looks rusty, odds are it’s starting to rust out: WOW OMG SON do I really get paid for this gig?

8. I doubt the mechanicals and electrics really care about inside vs. outside, but the cosmetics are another story. That said, my cars had to live outside for years, with no problems. I try to keep them waxed regularly, tinted my windows and use reflective windshield shades religiously.

9. Anywhere in the South or West where they don’t have much (if any) snow. Since this is a big concern for you, consider getting a quality rustproofing job when the vehicle lands in New York.

10. You don’t usually need to clean them, unless you over-oil a K&N filter or have a lot of PCV related issues. Many throttlebodies (TBs) have a coating that you simply cannot clean. My cars have very tidy MAFs and TBs, but they don’t sit around idling a whole lot, I know how to oil a K&N filter and they have well maintained PCV systems. Crudding/coking just ain’t gonna happen with me.

11. Anything EGR related is also a good idea. The EGR’s channels can be a big problem. And replace all rubber vacuum lines. I use a lot of carb cleaner (gloves, safety precautions, etc) to get the really tough stuff out of an intake manifold when off the motor.

12. Probably not, but again, a valid question for the forums. I wouldn’t trust the info elsewhere…especially from me!

13. Yes, it’s important to get all that crud out to ensure a perfectly performing drum brake. Wear a gas mask AND a poncho next time!

*Unless you have one of those Ford Explorers with the explody tires. The recommended 26psi in a truck like that was never a bright idea.

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry.

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2 of 21 comments
  • Robert Schwartz Robert Schwartz on Aug 01, 2012

    "the concept of pouring water in every drain hole and letting it freeze shut sounds like a great idea to me. ... Park outside when its salty out there." Wrong, Tex. Salt melts ice even if ambient temperatures are below freezing, that is why they spread it on roads. NY area does not get cold enough to where that would not be an issue, and cars in operation warm up. Also, a warm garage lets the goop melt and drip off which is far better than letting it stay in place, although there are garage maintenance issues.

  • SuperACG SuperACG on Aug 02, 2012

    Rear Drum brakes on a Mk4 Jetta???!!!??! MK4's got discs at all 4 corners. MK3s have the rear drums.\ Regarding tire pressure. I ran my MK4 Jetta TDI at 42-44 psi an all four corners. This was common practice among the TDI guys because it decreased rolling resistance, increasing MPG. Another member pointed out that you may lose traction, but I drove slow enough that it wasn't an issue. Living in San Diego, I didn't worry about rain. My current Ford Focus is spec'd at 32 psi at all tires, but I run about 35 psi. The tires are uni-directional and there is a void in the middle of the tire, so I don't want to overinflate too much.

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