Cleaning the IAB valve

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Thanks to Mike Killeen :

When my '92 developed a surging problem under constant (fixed) throttle, John Holowczak suggested that I clean the IAB according to the instructions on the FAQ. I never did find the instructions and it didn't look too tough, so I decided to take a couple of notes. This is not a difficult process and it yielded great improvements in power, economy and driving pleasure. The cause of the problem seemed to be a tank of bad gas.

The whole process took 1 hour, but hey, time is the penalty I pay for lack of skill.

Tools 5 mm Allen Wrench (a hex key to some).

  1. 2 Phillips head Screwdriver.

2 wrenches, both 1/2" (for battery cable). Optional - screwdriver body with a flexible 12" to 18" magnetic tip, just in case you drop something. Several (15 to 20) 6" foam tipped swabs with secure heads that won't fall off inside your engine. Tire marking crayon or nail polish. A can of Carb and Choke cleaner. These instructions. Disconnect the negative battery cable - this will also serve to clear the EEC, if you work as slowly as I do. Procedure

1) Locate the IAB, at the engine end of the throttle body, inside the connecting pipe between the left and right sides of the intake manifold, running front to back in relation to the car, but east to west over the engine, it is cylindrical in shape 1 1/2" wide by 3" long, with an electrical plug at the sensor end which you should unplug.

2) Slide the wire holding clasp off the IAB toward the firewall.

3) Mark the seam of the joint where the IAB meets the throttle body, mostly for orientation of the gasket because even I couldn't put the IAB on backwards.

4)Unscrew the Allen screws (seems a torx head will fit too) which run west to east toward the drivers side fender, loosen both screws but remove the top screw first, then turn the IAB toward the firewall to improve your access to the bottom screw (alternative method below if this dosen't work) - DON'T drop the screws. Use the crayon or nail polish to mark the seam that joins the IAB to the ISC sensor, to assure proper orientation when you re-install.

5) After removing the entire unit (IAB and ISC), unscrew the 2 Phillips head screws in the ISC. There is an O ring between the ISC sensor and the IAB - watch for it, mine stayed in the IAB, but it could be dropped and never missed. Clean the ISC (mechanical end only, not the electrical contacts - a dab of die electric grease will do).

6) The IAB has a spring loaded piston that is probably fouled black, hose it down with the carb and choke cleaner, then depress the piston and spray c&c cleaner through all 3 openings into the reservoir at the end of the piston - allow it to sit and soak for a suitable time (1 min. for me), then shake and repeat until you're satisfied that it's clean - use the foam tip swab as necessary. I was really into cleaning, so I sprayed c&c into the 2 throttle body ports left open by the absence of the IAB, then I got after the sludge with the foam tipped applicators - very rewarding in sludge removal but I made sure the tips were very secure before inserting them.

7) Clean the gasket between the IAB and throttle body. Re-installing the IAB w/o the ISC seemed to work best for me. The tricky part about re-installing was getting the bottom Allen screw started, I was able to insert it but had to have my daughter screw it halfway in by hand because my hand wouldn't fit and the clearance doesn't allow the Allen wrench to start it either - a most important point to follow - DON'T drop the screws!

8) Screw the bottom Allen about 3/4 in and start the top screw before going on to the ISC. Make sure the O ring is seated between the ISC and the IAB, install the Phillips (once again, DON'T drop the screws), slide the wire holder onto the IAB, attach the plug and finish screwing in the Allens and you're almost done!

9) If you work fast, you may want to insure a clean EEC memory by following the directions below: Per Doug Lewis, disconnect the negative cable, turn key to engine run, press brake pedal and hold for 30 seconds or so. Turn key to off and reconnect battery cable. The current drawn by the brake lights gently discharges any saved up electricity in the EEC-IV computer, and the computer then knows to relearn all the cars sensors, including either a partially clogged, cleaned, or replaced IAB (IAC).

There are 2 key ideas here,

DON'T drop the screws!!! This document is suitable for the author's use only. Anyone following the instructions listed above does so at their own risk. The author is not qualified to do this to his own car, let alone write instructions for you! Completing this process convinced me that I need to clean the intake manifold next...... Joshua Teixeira came up with a rather interesting way to get to that bottom screw if you've got lots of tools and some spare time ;-) :

You need:


5 mm allen wrench (which you already have from the top bolt) 1/4" universal 2 or 3 1/4" bit holders for a drill - total length 10" or so 1/4" socket 1/4 bit that fits the 5 mm screw head - 3/16" hex or a slightly larger torx bit works even better 1/4" handle, or 1/4" socket adaptor and battery drill short 1/4" extension If you don't have lots of bit holders, you can substitute 1/4" extensions The torx bit goes into the 10" of bit holders. The bit holders fit into the 1/4" socket which is attached to the universal. The 1/4" extension fits into the universal, and the 1/4" handle or the battery drill with the socket adaptor fits into the extension.

The idea is to have the 10" of bit holders and the torx/hex bit under the snakes (parallel and over top of the fuel rails), and fitting into the lower screw. The universal and 1/4" socket should be on the end of the bit holders in an opening in the snakes so you can plug the 1/4" handle with the extension into the universal. Once you have pre-loosened the lower bolt, you can use the assembly to quickly unscrew the lower bolt. You have to hold the universal from flopping around with your fingers, but it can be done. Judicious use of the battery drill on slow speed will make the job a little faster. Be careful that nothing flops around a scratches the paint on the snakes. Those with polished snakes don't need to worry about the paint scratches. <G>

Installation is the same as removal. Just do the final torquing with the allen wrench!

This method is guaranteed to eliminate the cursing at the lower bolt!