I've been driving myself crazy trying to figure out why my daughter's P5 idled at 1500 rpm and would pulse (or surge, or jump around, or go up and down) on deceleration. After finding that turning the air adjustment screw (AAS) all the way in had no effect (still high idle), and checking for vacuum leaks and finding none, I decided to let the dealer reflash the PCM (ECU) since the symptoms looked suspiciously like a TSB which required a reflash. (Here's the thread on that exciting episode...) But after all of this, I still had the same problem - high idle and pulsing rpm on deceleration.
Then I stumbled across a link about adjusting the Throttle Position Screw (TPS) (which I had done in an effort to try and solve this issue). This is the same screw that is referred to as the "Do Not Touch" hex head screw. This link led to a .pdf file (MA1213) from Mazda that described a procedure that had been used by techs to successfully reset the TPS. (Here's the link to that file (MA1213).) As I was reading through the steps, I noticed what turned out to be a very important note - "Be careful to not damage the factory-installed dark gray sealing compound in the throttle bore and on the throttle blade." What? Was that the same dark stuff that I had scraped out of the throat when I was cleaning the throttle body? Why yes... yes it was...
So, I had inadvertently committed two deadly sins on this throttle body - I had adjusted the TPS and had scraped out the "sealing compound" in the throat of the throttle body.
Turns out that Mazda (and Ford) set their throttle plates within the TB throats using the TPS first, leaving roughly a .001" gap, and then seal that gap with a compound called Dow 321 dry moly. This keeps air from being sucked around the throttle plate at idle, thus imitating a vacuum leak. A .001 gap doesn't seem like much, but the when it's applied around the circumference of the throttle plate, the total area of the gap exceeds the area of the AAS inlet (which is why adjusting the AAS had no effect). The real question was how I was going to replace the "sealant" that I had ignorantly removed.
I found a number of solutions on-line. First, the Dow 321 is very expensive and not available for retail sale here in the People's Republic, so I needed another option. I read that other dry moly applications worked, but I couldn't find any of the recommended brands locally. One guy had used spar varnish after first coating the throttle plate with vaseline as a release agent. Others have used nail polish or JB Weld. However, the method I chose was posted by a guy who used Permatex Gasket Maker #1 (which hardens and is resistant to fuel and solvents) and coating the throttle plate with WD-40 as a release agent. So I gave his method a try. Here's how I did it:
1. I set the throttle plate to a .001" gap as the MA1213 document stated.
2. I checked that the Throttle Position Sensor (TPS) was set so that it showed 1.25 kOhm at closed, and 4.61 kOhm at WOT. (Didn't need to adjust - Just figured I'd mention it.)
3. I cleaned the throttle body throat with TB cleaner followed by a wipe-down with rubbing (isoprophyl) alcohol. (Throat must be free of all oil residue)
4. Using a zip-tie, I tied the throttle plate in the open position. Then, using a small paint brush, applied a thin coat of WD-40 to the throttle plate outer circumference, wiping excess away gently.
5. With a toothpick, I applied a very thin coat of the Permatex #1 along the line where the plate closes in the throat, in front of the close direction of the plate.
6. Once I had this line of "sealant" in place, I slowly closed the plate into the line of sealant, and used a blunted toothpick to smooth the sealer into the plate and minimized the thickness of the sealer build-up.
7. After letting it set for about 30 minutes, I opened the throttle plate up, braking it free of the semi-cured sealant. (This is where the WD-40 "release agent" comes in.)
8. I re-tied the throttle plate in the open position and allowed the sealant to cure for 24 hours.
9. After curing, I used 400 grit sandpaper to LIGHTLY sand the sealant smooth, then closed the throttle plate multiple times to make sure it wasn't sticking.
10. Now the light test - Shining a flashlight through the throat should show very little, if any light. (Maybe a pin-point or two, but full dark is best.)
I re-installed the TB and the problem was solved! Car idled properly and and ran beautifully. AAS had proper function also. So if you commit the two deadly sins as I did (or even just one of them), hopefully this will help you get your P5 back in running order.
Melsman
Then I stumbled across a link about adjusting the Throttle Position Screw (TPS) (which I had done in an effort to try and solve this issue). This is the same screw that is referred to as the "Do Not Touch" hex head screw. This link led to a .pdf file (MA1213) from Mazda that described a procedure that had been used by techs to successfully reset the TPS. (Here's the link to that file (MA1213).) As I was reading through the steps, I noticed what turned out to be a very important note - "Be careful to not damage the factory-installed dark gray sealing compound in the throttle bore and on the throttle blade." What? Was that the same dark stuff that I had scraped out of the throat when I was cleaning the throttle body? Why yes... yes it was...
So, I had inadvertently committed two deadly sins on this throttle body - I had adjusted the TPS and had scraped out the "sealing compound" in the throat of the throttle body.
Turns out that Mazda (and Ford) set their throttle plates within the TB throats using the TPS first, leaving roughly a .001" gap, and then seal that gap with a compound called Dow 321 dry moly. This keeps air from being sucked around the throttle plate at idle, thus imitating a vacuum leak. A .001 gap doesn't seem like much, but the when it's applied around the circumference of the throttle plate, the total area of the gap exceeds the area of the AAS inlet (which is why adjusting the AAS had no effect). The real question was how I was going to replace the "sealant" that I had ignorantly removed.
I found a number of solutions on-line. First, the Dow 321 is very expensive and not available for retail sale here in the People's Republic, so I needed another option. I read that other dry moly applications worked, but I couldn't find any of the recommended brands locally. One guy had used spar varnish after first coating the throttle plate with vaseline as a release agent. Others have used nail polish or JB Weld. However, the method I chose was posted by a guy who used Permatex Gasket Maker #1 (which hardens and is resistant to fuel and solvents) and coating the throttle plate with WD-40 as a release agent. So I gave his method a try. Here's how I did it:
1. I set the throttle plate to a .001" gap as the MA1213 document stated.
2. I checked that the Throttle Position Sensor (TPS) was set so that it showed 1.25 kOhm at closed, and 4.61 kOhm at WOT. (Didn't need to adjust - Just figured I'd mention it.)
3. I cleaned the throttle body throat with TB cleaner followed by a wipe-down with rubbing (isoprophyl) alcohol. (Throat must be free of all oil residue)
4. Using a zip-tie, I tied the throttle plate in the open position. Then, using a small paint brush, applied a thin coat of WD-40 to the throttle plate outer circumference, wiping excess away gently.
5. With a toothpick, I applied a very thin coat of the Permatex #1 along the line where the plate closes in the throat, in front of the close direction of the plate.
6. Once I had this line of "sealant" in place, I slowly closed the plate into the line of sealant, and used a blunted toothpick to smooth the sealer into the plate and minimized the thickness of the sealer build-up.
7. After letting it set for about 30 minutes, I opened the throttle plate up, braking it free of the semi-cured sealant. (This is where the WD-40 "release agent" comes in.)
8. I re-tied the throttle plate in the open position and allowed the sealant to cure for 24 hours.
9. After curing, I used 400 grit sandpaper to LIGHTLY sand the sealant smooth, then closed the throttle plate multiple times to make sure it wasn't sticking.
10. Now the light test - Shining a flashlight through the throat should show very little, if any light. (Maybe a pin-point or two, but full dark is best.)
I re-installed the TB and the problem was solved! Car idled properly and and ran beautifully. AAS had proper function also. So if you commit the two deadly sins as I did (or even just one of them), hopefully this will help you get your P5 back in running order.
Melsman
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