After cleaning the idle air control valve for three years, the time between cleanings began to be reduced, so decided to replace with new. Online price apx. $171 vs. $230 locally (add $99 plus accessories for a simple 5 gal. dual tank air compressor to blow out the vacuum fittings on the throttle body). Here's where it is essential to have the factory service manuals. Wound up also cleaning the throttle body, adjusting the throttle positioner, and adjusting the throttle position sensor, +/- .004". Since I was only replacing the idle control valve to correct stumbling cold start up, one might assume the throttle position sensor and throttle positioner were fine, but since the manual lists various checks to be performed on and off the car when removing the throttle body, went ahead and checked. Surprisingly, the setting for the throttle position sensor (TPS) was not within specification. The last step is a verification - no continuity between the lower two contact pins on the TPS (with vacuum applied to hold back the throttle positioner) - at .028" and with continuity between those lower two pins at .020". Seems one essentially is checking the idle control switch function of the TPS. I had no continuity at .020", so loosened the adjustment screws and moved the TPS to achieve continuity - then re read the earlier section and discovered that the initial setting is to be done at .024", then the final check at .028 and .020 to confirm. So I re set it again, discovering the handy "continuity" function on the DMM which shows "OPEN" or "SHRT" on the display and sounds a beep for "short" - which with the leads clipped to the lower two contacts was actually the continuity I was adjusting to achieve - made it easier to slowly turn the TPS until hearing a beep sound. The throttle positioner is a vacuum operated diaphragm that holds open the throttle slightly until a vacuum is applied. The on car test with engine warm, is to run RPMs to 2,500, then release throttle and set positioner to 1,400 RPM, +/- 100. For some reason, mine was way too high. Adjustment involves using an 8mm wrench on the adjustment screw locking nut with very little room to turn it, but was able to get a bit more working room by lifting the spark plug wires out of the first clip. Throttle body cleaning: Can understand now, why Toyota techs remove the throttle body for cleaning rather than using Haynes carb. cleaner and rag method. First, the back side of the throttle body, that you cannot see unless removed, is far dirtier than the front. Seems the EGR port releasing exhaust, is right behind it. Also, when the throttle body (TB) is removed, you can see the teensy tiny holes - these things are really small - tiny, tiny holes that correspond to the vacuum fittings on top of the TB leading to the EGR vacuum modulator. Spraying carburetor cleaner through the fittings released a dark residue from the small openings in the TB throat. Also, of the two the idle air control valve (IAC) passageways, one had a lot of black color, though minimal buildup. This too, could only be cleaned by removal of the IAC valve after removing the TB. There was also a groove on the back of the TB with the black residue. And wiping with a rag, was able to remove quite a bit of black greasy residue from inside of the intake plenum directly behind the TB. BTW, covered the TPS with plastic prior to cleaning the TB with solvent spray. One more note, on the prior day's maintenance work, along with oil change, the factory manual lists specifications for accessory belt tension, and recommends checking regularly. I use a Burroughs belt tension gauge from eBay for the alternator/ AC belt, and a smaller click type belt tension gauge for the power steering belt. The A/C belt takes 130 lbs., +/- 10 lbs., and the power steering belt 80 lbs.. Both were loose and required adjustment. Thought I had tensioned the power steering belt about as tightly as I could 5,000 miles ago when replacing, but current reading was around 40 lbs. Discovered that by using a large screwdriver and prying against the adjustment bolt in the elongated slot, was able to exert sufficient pressure to bring belt tension up to 70 lbs. The A/C belt had been tensioned to spec when new, but also needed extra tightening. Using that Burroughs belt tension gauge has got to be the slickest way possible - one simply observes the disk with markings rotate and align the correct value with the pointer while turning the adjustment bolt for the belt. Frankly, don't see how these belts can be correctly adjusted without the use of gauges. Smoothness of operation and power both seem improved after this work. Could be subjective, but in any event, car drives beautifully. Gave me an appreciation for the work the Toyota techs perform if they actually do the prescribed work from the service manual, IAC valve replacement and TB cleaning and adjustments would be worth the $350 I've seen referenced here. Speaking of Toyota techs, one final footnote. While removing the screws holding the IAC valve, I used a hand held impact wrench operated with hammer strike to the end to loosen Phillips head screws without stripping them. Had acquired this tool many years ago for removing stuck screws from motorcycle cases. Anyway, the first three of the four came out effortlessly, but the fourth screw head became hopelessly rounded such that the "cross" in the middle turned into a nice little circle. After removal with vice grip pliers and a trip to Toyota parts dealer for replacement, they could only special order. Not sure this procedure is accepted practice, but walked back to the service bays with stripped screw in hand - after being declined by the first mechanic, a kindly second mechanic nearby asked about the problem as I began to walk away and wound up finding an exact replacement from his extra parts bin and grinding and buffing the threaded end to match length. Very nice work on a critical fastener - much appreciated.
- posted
19 years ago