Smoke at idle fixes, my thoughts and notes

[bnoon]

This is going to be my thoughts/views on the known fixes for the common "smoke at idle" issue. Seems like a get this question at least once a week, so I thought I'd try to condense all my knowledge on the subject to one thread. This is NOT for smoke under WOT or puffs during shifts as the two are not related. I will add/modify/delete for revisions as needed.

In my own personal experience, I started smoking at between 1,000-1,500 miles on the car. This was on the 2 mile trip home immediately after installing my catless DP/RP combo. I had also installed a custom intake at about 100 miles on the car and that didn't make the car smoke at all by itself, but for sure contributed to it by decreasing the vacuum on the intake tubing due to removing the restrictive air box and filter. Think of the PCV system as two ends of a straw with one person sucking on each end. The intake manifold end sucks harder than the TIP end, but BOTH contribute to how much vacuum the crankcase sees. Since the intake manifold end has more vacuum at idle, the flows from the intake boot, through the valve cover, through the crankcase, and and then enters into the engine through the intake manifold barb. Flow under boost will reverse towards the turbo because the PCV closes under boost, the turbo inlet side suction increases as the turbo spools up, which is why we get a little residue in the inlet side of the intake boot. If you have more than just a little residue, you have other issues outside of what will be discussed here.

• Thicker Oil - This worked for me initially, but once the oil got about 1,000 miles or so on it, there would be smoke again. I tried every brand I could think of, cheap to ka-ching, everything smoked eventually and all well before the 3,000 mile change intervals I was using. One thing to note: Royal Purple has my vote. Not that it did any better at preventing the smoke, but that when it did smoke it smelled the best.
  

• Catch can - This didn't do diddly poop for my smoke at idle. I had thought that it worked initially, but after about 100 miles or so I was smoking again. I used the Saikou Michi catch can and Cobb's installation instructions, which called for a second PCV valve installed onto the manifold barb. While it did improve the condition of the oil itself, it did nothing for my smoke issue. In fact, later testing showed that it dropped vacuum to the crankcase adding the second PCV valve due to the restriction of flowing through two PCV valves. MATT DAMOND had switched to a check valve in his kits shortly after I installed my catch can, so I tried that as well and no change on my smoke issue. My testing showed that both of my stock PCV valves would seal to well over 40 psi without leaking. Perhaps those people that this fix worked for were boosting into the crankcase past a dirty/leaky PCV valve? Also, on a related note: Catch can warning for cold climates!!!. Be sure to empty them often in cold climates and/or come up with a way to warm the CC up before emptying it!
  

• Restrictor bolt (AKA bnoon bolt) - I took something from another member's comment that went something like "If someone makes an oil restrictor for our cars, they would clean up". I thought back to my turbo Dodge days from the 80's and we sure did have to run restrictors inline to not smoke on those large turbo swaps too. Could it really be that simple? I started by taking my PTP SST with me to the local auto parts store (The SST was later sold and never installed) and found the thread size/pitch of the oil feed, then a trip to the hardware store for precision drill bits. Install and how to here Oil restrictor bolt install. Initially, I did a .090" hole and got the smoke to drop down quite a bit from the stock bolt. I was waiting to hear back from several rebuilders to see what they recommended for restrictor size and everyone agreed at .060". I didn't try the .060" until after the PTP pill failed to work for me under all conditions. Here's a video of the first oil restrictor bolt that I installed with a .090" hole. It was a step in the right direction as before this install it looked like a bee keeper bug bomb went off and you couldn't even see the back of the car. The .060" and raised idle don't smoke at all
  YouTube - 100 0361

  YouTube - 100 0361

  .
  

• PTP Pill - I tried this next because I was still leery about restricting the flow of the turbo's oil feed because I had done the bolt before I had heard back from the rebuild gurus (which later turned out to be well within the safe range). In theory this PTP would work to increase vacuum across the crankcase by restricting the intake side of flow. But how could this work as vacuum added to vacuum = more vacuum and the pill is restricting vacuum from the inlet side, right? It's a weird phenomenon known as venturi effect. Think of it as a straw that you partially block with a finger as you suck on one end... you can collapse the straw as vacuum from your mouth (intake) increases as the finger (PTP pill) actually restricts overall flow... Upon first install, I still had the .090" restrictor bolt in place. The pill did seem to help initially and was strong in theory, but I was still getting smoking under trailing throttle and at long idle periods (like fast food drive through). Once I combined it with my .060" size bolt, everything was good for quite a while.
  

• Raise the idle - Once ATR came out from Cobb, I had heard from other members here about raising the idle as a smoke fix. Once I finally got an AP with ATR for myself this winter, I decided to do some testing/logging and found that idle vacuum at the factory idle was pretty low at about 8.5 PSI. When I raised the idle to 1,000 RPM, that idle vacuum jumped to just under 11 PSI!!! Raising it higher gained no more vacuum, so that's where I left it. Removing my bolt though made the car smoke again under trailing throttle and when the AC was on. When in defrost and AC modes, it kicks the AC compressor on and increases load at idle, that opens the throttle blade a little more to maintain 1,000 RPM idle, which drops vacuum down to high 9's = enough for my car to smoke during the AC duty cycle. My PTP pill is removed and I now run 5-30 oil again.
  

• Factory Mazda fixes - Turbo - The first fixes from Mazda were replaced turbos. I had mine replaced twice before my semi-mod friendly dealer told me "No more" and I still smoked. The improved seal design may work for some, but it did nothing for me.
  

• Factory Mazda fixes - Redesigned valve cover, TIP, and reflash - While I have not had this fix done due to an aftermarket TIP installed and me not smoking anymore, I still feel that this is a fix in the right direction for those within the factory warranty or those not wanting to get too crazy with the modifications. In theory it will work by moving the upper PCV hose to a higher vacuum area of the intake. Back to the straw analogy, think of it as one person on each end of a straw sucking, with the person on the upper intake end sucking a little harder than before.
  
  I don't know if everyone gets the reflash, and I haven't seen the reflashed settings... but what do you want to bet that it raises the idle?

Ugh... enough typing for now.