pearlpurple

As in subject line code 26 Quad Driver fault

Just happened last night on my way to the show & shine. When I shut it down, restart it it takes a minute for the SES to come back on.

Car has sat for 4+ months

141k miles

Air pump replaced a couple of years ago

O2 sensors have less than 50k miles on them.

Idles at 500 rpm so not sure if related???

Starts rough when hot have to crank it for say 3 or 4 seconds then it will go but idles low at 500 rpm. Cold start normal. Runs fine no misses, good throttle response no drivability issues. Car is never abused.

My research (googled) says EGR/EVAP/AIR PUMP are typical.

Fans do run so not the fans

Car is basically stock, no changes to any emissions stuff, everything as it would be from factory other than CAI/shaved heads/u/drive crank pulley/ OBD1 chip/aftermarket exhaust. Car had run with these items for years so nothing new has been added in over half a decade.

I have a complete spare LT1 engine in a cradle with full parts including intake with egr & throttle position or IAC solenoids. If it is a solenoid removing one from my spare engine (assuming solenoids are good) would clear the code if I simply just plugged it in? May help me troubleshoot?

My car sits a lot as in 2 - 3 or more months at time as I don't get to drive it much. Car is in really good condition, under the hood very clean car is taken care of really well no butchered wires, no grease all over etc. etc.

Any commonalities from above info before I start?

Thanks for any help.

Injuneer

DTC 26 can be due to the AIR pump electrical circuit, the EGR vacuum solenoid circuit, or the EVAP purge solenoid circuit.

Most common cause is a blown fuse for the AIR pump.

Shoebox has the best LT1 specific code list. Note that 93 codes can be different from 94/95. Look at the column on the far right for the differences:

http://shbox.com/1/Dtcs.htm

Plugging in a "good" solenoid will not clear the code. And you would have to drive the car under conditions that allow the diagnostic for the code to be run.

pearlpurple

Thanks Fred.

One question around the low rpm at idle. Which one of the three might have the higher probability of causing the lower idle rpm? I had the air pump go out a couple of years a go and replaced it with a new one and at that time the idle rpm was not impacted.

I am going to troubleshoot next weekend.

Thanks again.

Injuneer

Those are all electrical circuit faults. On the AIR pump it's for the signal side of the relay. You can remove the AIR pump completely and you don't get a code as long as there is a good fuse in the circuit. AIR only runs for a couple minutes at startup, so it isn't going to affect idle.

Neither EGR or EVAP are used at idle, so I can't see any connection there.

Since you have an A4 the stock ECM idle setting, engine fully warmed up, is 550 RPM in drive and 650 RPM in neutral. What is your "OBD-1 chip"? If it's a reprogrammed chip, I doubt anyone would have lowered the idle speed. Hence, no codes related to IAC.

Idle speed is controlled by the IAC. It's not a solenoid. It's a small stepper motor that moves a pintle in and out of the air passage to control flow. In response to an incorrect idle speed, the PCM tells the IAC how many steps it should be open, until the idle speed is correct. A scanner can read the commanded IAC position, but there is no feedback as to the actual position, or even whether the IAC is working.

If idle is below spec, the ECM will increase the IAC "count" (number of steps open). The max count is 160. If you can find an OBD-1 scanner that can read IAC counts, you can watch the ECM respond to low idle. If the IAC counts max out at 160 and the idle is still below spec, you know either the IAC isn't working, the idle air passage is plugged, or the wiring or connector is bad.

You can scan and run a data log using a free program called Scan9495. Free download in a "sticky" at the top of the "Computer Diagnostics.... " forum. Will need to buy a cable. The author is a regular on this site and can help with install and functional questions. I can help with interpreting your data log.

pearlpurple

Finally got to take a look and the smog pump fuse blown. Replaced fuse, blew again. Unplugged, replaced fuse and not blowing so I am going to assume smog pump. Thing is I changed this thing a couple of years a go and I have not put more than 2k miles on the car since or even less. Oh well ordered a new one.

On the idle thing when I started it up cold it didn't want to run until it warmed up properly and then ran fine. Opposite to what I saw the other night.

Thanks

Injuneer

Is there any particular reason you want a working AIR pump? It only runs for a couple minutes at startup to help the cat heat up faster and start working.

Could have a problem with one or both of the check valves leaking. If exhaust flows backwards into the pump, the water in the exhaust gasses condenses and the pump starts to rust.

pearlpurple

I want to keep the car as emissions compliant ready. I have moved around a lot in my career and am not sure where next. If that happens to be a stricter state or province I don't want to have to play catch up. My car is pretty stock with the exceptions a few little things but under the hood everything is still there and still functions like from the factory. Only obvious difference is the CAI and I have the original intake system in the garage.

To test said check valves I should be able to simply remove the air pump and see if exhaust gases are back flowing correct?

Thanks again.

pearlpurple

Interesting this morning the car started up perfect, ran fast idle as it should, came off fast idle as it should and exhibited no issues at all. Hmmmm.

Injuneer

Leaking check valve will sometimes melt the rubber hoses in the system. The 93 AIR plumbing is totally different than 94-97, so I can't recall if that would be as obvious on your setup as it is 94-97.

Most tailpipe emissions tests do not test the engine under cold start conditions, so they have no way of knowing whether the system is working or not. As long as all the equipment is there and connected, it will pass visual. I'm not encouraging non-compliance. But spending a lot of $$$$ on a new pump seems unproductive. I took my AIR system off when the car became a "track" car, and the pump was still in good shape after maybe 12 years.

pearlpurple

I do get your logic Fred thanks. It is just me as I have been able to keep the old girl pretty much stock & in tact like from the factory. After 140k miles still original paint, motor/trans never been out, original wtr pmp, opti, fuel pmp etc. etc. I have replacements for above mentioned plus more as I expected them to go out by now.