MAP/MAF DTCs - sensing engine torque problem

[justdave]

Have a 99 Bonneville Se with 163000 miles on it. Recently had DTC light, after problems with Overdrive Lockup torque-converter doing the 'shudder' on a very slight incline of highway at 65MPH with CrusieControl engaged. Otherwise the car had been driving fine.
Fuel-pressure was found to be low; i.e. - engine had not been making enough torque for the transaxle Computer-controller to be able to correctly tell it WHEN to shift; it had not been getting sensor information that was within it's Factory 'map' of program-code, we figure.
Replaced the fuel-pressure regulator, and car was then driving normally again, shifting in and out of Lock-Up on the Highway correctly, and on back roads at lower speeds was also shifting into lower gears (from OD) for hills, automatically.
All was wonderful...until we drove it 107 miles. Then got the Check Engine light on dash again. DTCs were pulled at Autozone:
P0102 - MAF - Circuit A voltage low
P1106 - MAP- (*different DTC than previously) - "Engine operating within Failure Mode Test conditions and the ECM detected the MAP sensor voltage was above 4.8 volts".
*Note that these are Autozone-generated blurbs about the codes, NOT directly from G.M./FSM.
The MAP blurb implies that the engine is operating in a Failure Mode. Anyone with GM technician experience or with a GM FSM, know exactly what that might be?
*I DID perform an "Emissions Test Readiness Monitor" drive-cycle specifically, earlier, after work was completed on the car and the battery was re-connected. [ "With fully warmed engine, from a stop, accelerate to 50-to-55MPH using 1/2 to 3/4 throttle, and hold that speed steady for 5 or 6 minutes, have rear defroster "ON" if equipped. After above conditions are met, stop quickly (use caution re other drivers behind you), then accelerate again as above, to 55MPH..then coast, to below 20MPH, foot off brake and throttle (manual trans cars placed into neutral)". ]
I am guessing that the engine is either still not making (just) enough torque, to generate MAF and MAP sensor signals that are within the range which the computer program code is able to use successfully...or...one of the sensors actually IS faulty at the specific difficult detecting conditions
(engine at 1600 RPM, car at 65 MPH, trans in OD/Lockup, reaching a very slight highway incline).
Any thoughts?? Any technical information for me re either MAF or MAP sensor?? (Both WERE cleaned, carefully and correctly, when we did the other work.) Both are WORKING just fine during ALL other driving conditions. I am not going to just go out and buy new non-returnable Sensors without a VERY good technical/proven reason for doing so.

[myfirstbonnie]

Unplug the MAF and see how it runs with it unplugged.

[justdave]

Already did that, waay back...AT IDLE ONLY, engine already running, unplugging the MAF leads to idle going up and down, 1300 to 500 to 1200 to 550 repeated and eventually settling down at 900RPM. Engine is not happy about it, but 'can' still idle more or less. [I.e.- the IAC and PCM doing their jobs.]
Have NOT driven the car with the MAF unplugged (nor will i), nor attempted to start the car with it unplugged.
May i ask exactly what diagnostic information one would obtain by unplugging the MAF?? What are the various outcomes of doing that 'test'??

[myfirstbonnie]

Unplugging the MAF makes the PCM use the default tables. If the issue goes away with it unplugged then you probably have a bad MAF.

It will not hurt to drive it with it unplugged.

[justdave]

It has been awhile since last post. First, a thankyou to everyone for your replys.-----The mysteries have been solved for this particular 99 Bonne SE with 'K' code engine. Am posting info here in hopes that others will be helped.-----As might be expected with an old GM car with so many 'normally-occuring' (known common) problems...the solution required multiple fixes.-----The catalytic converter was plugged enough to have been causing excess engine heat, even though the honeycomb 'looked' OK when removed. After replacement with a universal braze-on type, engine temps went down very noticeably on the dash gauge.-----The M.A.P. and M.A.F. sensors were (eventually) proven to be just fine, DESPITE having DTCs generated that pointed to them; i am SO glad that i resisted buying new sensors.-----One of the three ignition coils had been replaced previously by another owner, so i pulled the entire 'Coil Pack' assembly (Coils/I.C.M./bracket), field-stripped it, and cleaned EVERYthing (including corrosion areas on the aluminum). While trying to check the resistance of each coil's Primary and Secondary windings, i discovered that the internal female connectors (inaccessible/covered by a molded-in-place plastic insulator) were 'loose' in the sense that they no longer fit tightly onto the corresponding male 'blades' sticking up from the IgnitionControlModule. (I had put temporary blade connectors into the openings, and had difficulty getting solid readings.) I did eventually find that the Secondary resistance of the non-GM coil was 6.08Kohms, while both of the Factory Gm coils had 5.77Kohms. That is 'non-matching', but was it 'close enough' to NOT cause misfires (as other have found occurring when mixed Ignition Coils are in place)??-----To "fix" the loose Coil-to-ICM connections (since i had no access to the female connectors themselves to tighten them up the usual way with a pair of needlenose pliers), i simply twisted all six male blades on the ICM, rotating them 5 degrees at their tips (only) with a pair of "smooth jaw" pliers. (Do not scratch the connector blades with normal serrated-jaw pliers.) When plugged back into place gently (while wiggling them a bit), the Coils each seated onto the blade-connectors just fine. *Use some silicone di-electric grease around the six connectors to keep water out*-----The above simple procedure is highly recommended (for every engine with similar connectors), because it CURED the "misfires" DTC...and made the MAP and MAF diagnostic trouble codes go away TOO!-----One more little bit of info: found a 'small' 1/2 inch Hg vacuum leak in my EVAP system (above the charcoal canister), only by using a Vacuum Gauge and watching the dial carefully. Note that no EVAP-related DTCs were ever generated. Replaced a rubber connector that 'looked' perfectly fine, but actually was crumbling (when removed and flexed with fingers). *Actually, i chose to replace the rubber connector and the black nylon tube leading to it...with a length of reinforced rubber hose.-----**Tips and Word of Caution: to access the Canister-top area on this particular Bonneville, one has to remove the air-filter housing, and then move aside the 2 computers encased in a double-cover enclosure. The assembly is attached to the body metal with two unique black plastic 'fasteners' (designed by GM to "not" be removable by owners). In my case, i chose to rip them out with needlenose pliers; be careful not to crack the brittle-with-age plastic flanges under the fasteners; i re-fastened when done with real sheet-metal screws (short length, to avoid harming anything beneath). The caution is two-fold: avoid excess movement of the 2 large wiring harnesses going into the assembly...and make sure the inner cover is positioned correctly (to seal against the rubber seal on the lower half; this task is made a bit difficult by the stiffness of the 2 wiring harnesses)...and get the outer cover secured in place firmly (to retain the inner cover, it must be). In my case, the old black plastic outer cover was warped AND had one of the three retaining 'clips' (mickey-mouse design) broken-off; i had to tie it firmly in place using some plastic twine (be sure you do not wrap around any of the EVAP hoses that lie underneath the computerbox assembly, as you are tying the cover in place). If you are lucky, the double covers will still be firmly in place, and you won't have to monkey around with them, as you move the assembly aside to get access beneath it.

[maroon111993]

I have this in my 97 GP GTP. Unplugged the sensor and it runs the same.... Same code and engine light. Any suggestions on what to check? Doesn't run any different.

[maroon111993]

And just found out today I'm only getting half boost from the SC. Any ideas/suggestions?

[myfirstbonnie]

You need to start your own thread explaining any symptoms and codes you are getting. Also specify any work that has been done to it recently.

This will get the proper attention to your needs.

[maroon111993]

Just did this last night. Thanks.