I've been trying to trace down an issue that seems to stem from idle speed or throttle and could use a hand.

92 RS LO3 auto. Engine was rebuilt about 35k miles ago. PROM 1228746.

Bit of backstory. Last summer had a symptom of coding (never actually pulled it...) with sluggish response and occasional stalling at low gear. That was cleared up by a series of iac, tps, coil, ignition module, a bad plug wire, and things were good till it started up this new tantrum. The TPS I put in last year was a cheapo 'what they had at oreilly that day'.

Started throwing a code again about a month ago along with symptom of surging and sluggish throttle response. When it would ses, if I was at low gear/speed (maybe less than 35mph-ish) I could completely let off the throttle and either go a good 1/4 mile without losing any speed or twice I actually gained speed. Finally admitted I won't be doing an ls1 swap soon enough and bought the Moates aldl cable with usb. Soon after that admitted temporary defeat and added a win7 dualboot to my laptop. (anyone with a working setup on any linux distro I'd love a pm from - and super bonus points for Debian. I got winaldl launching but still fighting the serial settings in wine. have not yet tried the native ftdi drivers though.)

When I started this prcess I was just throwing 22, low TPS. Tested out the wiring and the ECM, also tried the spare ECM I have, same PROM just original vs 3yr old delco. All wiring good on the multimeter, except when plugged into the back of the TPS I would occasionally get a 0.1 or 0.2. Replaced cheap TPS with a delco. Went thru the full reset process, set idle to ~450, reconnected IAC. Can't adjust the TPS that I can see how to - screw locations allow zero motion. Drove around fine for about 120 miles. Then all of a sudden driving home from work Wednesday it goes SES, throttle goes sluggish, and idle won't drop below 1500 at coasting, braked, neutral, park. Let it cool down and ran it around the neighborhood, same thing except it would drop to around 1100 at lowest (per winaldl and tach) and when I put it back in the driveway and tested throwing it in neutral it jumped to about 1700.

I still haven't gotten TunerProRT to recognize my cable, though winaldl sees it just fine, so I'm only able to see what sensor data is on the screen right when I look which eliminates gathering much from driving around. I did have it hooked up though and when I got back it had thrown 22, 34, 43 - low tps, low map, esc. Went back through the idle reset process today. Jumpered the aldl input to Dx mode, pulled the IAC, ignition off, pull the jumper, plugged the aldl-usb back in. Managed to turn it over and had about 350 RPM for the half a second or so before it died. Turned it back up to 475 and verified on winaldl it was maintaining at 475-500 in idle/park. With that holding steady for a while, revved the engine a bit, then gave it wot. TPS reads 0.57 at idle but 1.45-1.78v on wot on winaldl on various tries. What's interesting to me there is it never throws a 21/high TPS - even though I kept it revved up for a few seconds waiting for it to do so. MAP avg and max voltage is 4.7. Plugging the IAC back in, turned it over, immediately resulted in 1050 rpm idle.

I've about hit the ceiling of where I know to go with it past 'start replacing parts and doing trial and error'. Is it worth replacing the MAP? Am I missing some part of the 'move the TPS up and down' process since mine has no room to do so that I can see? Most of the mechanicals on the car have been replaced or rebuilt in the last 4 years and I haven't found any vacuum leaks, though that warrants another look. Planning to try to do so soonish, requires braving the heat again though. I'm thinking at this point it's got to be a sensor or tuning/adjustment I'm just not sure which ones to try/test. If there's specific data I can grab from winaldl I'm happy to do so, just not sure what to be looking for yet as I learn my way around using it.

I'd also be interested to any insights on why winaldl would recognize my cable but tunerpro does not, though I realize that's probably a separate post to the diyprom or ecm boards. I've got the ftdi driver installed (2.08.24), com3 is set to 4800 baud (didn't like 9600 baud either, nor 2400). Win7 64. I plan to fight with it some more as I can, but the biggest problem is the car likes to throw these fits at me in the summer. It's generally around 110* in the day, 90+ over night, and I prefer to not have to either run a powered USB hub out through the garage so I can extend the cable into the house, or buy/build a cold-case for the laptop, so I'm limited to brief stints till about October. Side note, if anyone in Phx metro is inclined to lend a hand with sorting out the datalogging, PM me.

 

Sounds like the exact same thing that is going on with my car. I dont have a considerable backround in auto mechanics or codes, so when it gets to electrical I have no clue what to do, Which is ironic given that my father is an auto mechanic and professional electrician.

 

Seem to have achieved some improvement. Checked, still no vacuum leaks. Pulled the IAC out to check if maybe it had gotten messed up in some way, spindle wedged, etc. Found it in good physical shape but gunked up pretty bad. I cleaned out the throttle body and air intakes last year so it shouldn't have been that gummed up, in theory. Cleaned that up as well as I could without putting any pressure on the spring or spindle, and gave the intake a good blast of throttle body cleaner. Screwed the IAC back in, and did a reset of just the IAC by depressing the accelerator slightly, then turning the engine over and leaving it on with the accelerator held for 5 seconds, turned if off for about 10 seconds. Idle was around 900 when I cranked it back over. Took it out for a spin to reset the ECM, surface streets, freeway, surface streets, parked, and back again - all with the AC off. While wholly unpleasant (at least it's overcast today) the chilton's indicates this is the operating parameters expected when resetting the IAC. Shrug, maybe it was use of the AC when last I reset the idle that threw it off, but I'd be real interested to know how that factors in.

We'll see how it goes next few times I drive it. I'm not totally sold that it's fixed yet, but it's better right now anyway. Suspect it may be running rich too, last time I refilled the tank I'd only averaged about 14mpg, and with fairly new fuel filter/pump and clean tbi I shouldn't be finding things that gunked up.

 

Cool. I'm going to mess around with mine when it stops raining. Might get some Sea Foam and clean out the vacume lines and everything.