Boss96

Hi guys, I'm pretty new to Camaros and need some help. This is a 92 RS with 305 TBI.
The problem is that it won't hold idle when I start it. It will go to 1200 rpm or so at first, start to slow down and then either stall out right away or start surging up and down and then stall.
Pulled a code 33, MAP sensor problem. I checked the signal voltage at the sensor when it would hold an idle for a few seconds and it was about 1.3 volts which seemed to be in range. Checked the CTS sensor (car was warm at this point) and it was about the same voltage give or take.
In the Chiltons book it indicated that the code 33 could be set by having a rough idle, etc, so the sensor may not be the actual problem. I removed the egr valve, cleaned it, even blocked it off temporarily to no avail. Removed the idle air bypass valve and cleaned it too. Checked the tps voltage, low when closed throttle, voltage goes up when throttle opened up.
I should mention that when the engine was cold it did start but had a very high idle and lots of surging. After letting it run for awhile like that I restarted it and got the above symptoms.
I can't find any vacuum leaks, I have blocked off all the vacuum ports at the TB and found nothing. The only thing that seems to make a difference is disconnecting the vacuum line to the MAP sensor and the idle will smooth out for a short time but start stalling again. Holding the throttle open will keep it running but it seems to be very rich from the smell of the exhaust.
Should I change the MAP sensor or am I missing something?
Bob

ShiftyCapone

iTrader: (7)

These surging problems seem to come up all the time and are always the hardest to diagnose. Well if the car still ran like poo with the MAP plugged I would noramlly look at something related to timing or ignition related (module, dizzy pick up, or ESC). However, since it ran better I would look into replacing the MAP. You did get a code for it along with a little idea of its behavior when plugging it. What is the basic state of tune of the car. I assume all plug wires are okay, base timing is solid, and plugs are normal?

Oh and by the way, welcome aboard my friend.

Boss96

Thanks for the quick reply
Plugs and wires I'm not sure about but since the idle will smooth out to just about normal (for a short time) when pulling the vacuum to the MAP I assume they are working ok.
The problem seems to be intermittent (until now anyway) as it would run fine then go to this problem randomly but then go away.
I'll try the MAP tomorrow and let you guys know.
Bob

ShiftyCapone

iTrader: (7)

What is the condition of the 02 sensor? A bad 02 can cause your problems without throwing a code.

Boss96

The 02 sensor is probably old so it could certainly be changed out. But...the intermittent problem recently before whatever it is failed? Also, the 02 does nothing when the car is cold, correct?
I'll gladly change it if that is what is needed though.
Thanks again,
Bob

ShiftyCapone

iTrader: (7)

Correct. However it may outrule a future problem if it needs to be replaced. Just added insurance. I don't suspect that since your problem occurs during both open and closed loop operation.

Boss96

Well, changed the MAP sensor tonight and it did not fix it. Had a friend come over ( at tech) and he disconnected the tps as well as the MAP sensor and the car ran..It would not run with either one reconnected.
Maybe this is obvious, but should I change the tps then?
Weird.
Bob

ShiftyCapone

iTrader: (7)

Just check the voltage first to see if it is within range.

Boss96

That's the strange thing, I had checked it and it seemed ok. I guess I'll get a new one today and see what happens. I imagine I can return them if they don't do anything.
Bob

89305RS

you normally cant return anything electrical to a prts store after use.

FirebirdNYC

how did ur buddy disconnect the tps and map?...or did he just unplug it, reason why im asking is because im having the same problem, damn mechanic on vacation ..car was like this 2 weeks ago, got it back fixed then it started again

Boss96

Well, it's not the tps sensor According to the chilton book, disconnecting the map sensor will make th ecm use the tps sensor for fuel settings but in my case that won't work unless I unplug the tps also.
With those sensors disconnected the car will idle fine so I doubt spark is an issue.
At this point, with sensors connected, the car will start for a second and then just stall out.
I rechecked the cts and the resistance was about right for the engine temp.
One thing I did not mention is the oil pressure gauge is not working, I made sure I had oil pressure though by looking through the oil fill hole and saw oil flowing along the bottom of the valve spring area. I read that if some pulse is missing from the distributor the ecm will shut off the fuel pump relay and use the oil pressure sender to turn the pump on if there is oil pressure. I just bypassed the pump relay so it was on all the time and again no good. BTW, I noticed some kind of sensor on the drivers side of the block, close to the ex. manifold, it uses a connector that just slides on, not a push on type. What does that one do? It appears to be some kind of coolant temp sensor but there is a coolant sensor on top of the intake so I don't know what this one does. I'm not referring to the oil sender.
I'm stumped, what's left?
Bob

FirebirdNYC

that sensor is the coolant temperature switch, that has nothing to do with the ecm, it actually connects to the guage

ShiftyCapone

iTrader: (7)

Yup. It is the xsending unit for the gage out put. The CTS and fan switch are the other 2 coolant related sensors.

FirebirdNYC

so confusing there all basically the same expect they have different connections

ShiftyCapone

iTrader: (7)

The sending unit tells the gage what to read. Same thing as the oil sending unit. The CTS reads the coolant temp in the manifold and the ECM uses those values. The fan switch will monitor water temp in the head and kick the fans on when things get to hot. A broken sending unit and or fan switch will not cause your car rto run bad. The CTS is the most crutial coolant feedback device.

Boss96

Here's the latest. I talked to a Chevy tech, he said it probably is the fuel pump/filter. Reason it runs ok with the 2 sensors disconnected is the ecm commands more fuel under those conditions. I suppose if I had driven it that way I would have seen it go lean under any kind of load from the weak pump. It could also still be the oil sender too since it controls the pump relay but that is not so likely as the car has been running in the past with no indicator showing oil pressure.
I'll let you guys know what I find.
Bob

Boss96

BTW, where is the fuel pump? In the tank I suppose or is it an external one?
Bob

FirebirdNYC

i believe its in the actual tank

TBI92

So, what did you figure out? My 89 350 TBI is having the exact same problem - unhook the MAP and it idles steady, hook it up and it surges and stalls.

Was it fuel pump or regulator? Let us know what you figured out!

Boss96

It was the fuel pump, actually the rubber hose that connects the actual pump to the metal fuel line. Since you have to drop the gas tank to fix it I changed the whole pump anyway.
Bob