93 Beretta Rough Idle, Please Help!!!!!!!

Hi all, just bought a 93 Beretta... nice little car, but it has a couple issues I need help with.

Car sat for 3 years without being started, and had little to no fuel in the tank. Tried jumping it (battery was beyond saving) and finally fired with a fresh battery. However, after 5 miles, the car wouldn't idle. I ran 93 mixed with SeaFoam through it to clean the fuel system, and it didn't help. I cleaned the throttle body, and that didn't help either.

I then tuned the car up, and it set codes 33, 35, and 44. 33 indicates MAP sensor signal voltage is too low, 35 indicates IAC circuit, 44 indicates lean exhaust. I replaced the IAC and reset the computer, 33 came back.

I then had the car scanned (supposedly) by a shop, which told me the MAP sensor was bad. I swapped the MAP sensor from my 92 Z-24, and that didn't help the problem. The dealer told me these two model years use the same sensor, but none of the #s on the two sensors match.

I have to hold the throttle slightly open to start the engine, and occasionally, it will idle fine from a start, problem is starting to seem to be related to engine temperature. The coolant temperature gauge reads kind of low going down the road, but will heat up when idling. Averaged 27 mpg over the last tank, is this normal?

I like this car, but it is driving me crazy!!!! HELP!:banghead:

bad hose from the intake to the map sensor, try this take hose off at map, crank over, see if you have vacuum...

bad hose from the intake to the map sensor, try this take hose off at map, crank over, see if you have vacuum...

I can't believe I didn't think of this... :screwy: Thanks, this helped immensely.... There was no vacuum at all.... Bypassed by drawing vacuum from another source.....Still have to set the idle speed a bit high, I guess I will have to pull the upper plenum and repair the original hose?

Also have some jerking on downshift when braking, disconnected the TCC harness and it went away, could the small vacuum leak from the original MAP hose source be causing it?

The vacuum leak from the original MAP sensor line is probably the cause of your high idle, but may or may not be the cause of your trans jerking on downshifts. Since unplugging the TCC stopped the jerking, I'd bet the TCC solenoid is sticking causing it.

>>>>Mankind needs a natural predator that stalks the stupid!


Amen. :grinyes:

I can't believe I didn't think of this... :screwy: Thanks, this helped immensely.... There was no vacuum at all.... Bypassed by drawing vacuum from another source.....Still have to set the idle speed a bit high, I guess I will have to pull the upper plenum and repair the original hose?

Also have some jerking on downshift when braking, disconnected the TCC harness and it went away, could the small vacuum leak from the original MAP hose source be causing it?glad i had a good suggestion, btw the tcc on the 3 speed auto suck, try a trans flush see if that helps...

The car is running better than it was, but still not quite right... I do not have vacuum on the line that goes down the front of the engine to the evap canister either... I suspect I am going to have to pull the upper plenum again... Am I correct in assuming that all vacuum hoses draw from the lower plenum except for the PCV?

The car is running better than it was, but still not quite right... I do not have vacuum on the line that goes down the front of the engine to the evap canister either... I suspect I am going to have to pull the upper plenum again... Am I correct in assuming that all vacuum hoses draw from the lower plenum except for the PCV?is this vacuum canister you speak of on the front of the trans?... or does it actually go to a canister (black plastic), if it goes to the canister the is a electric solenoid in that line....

It goes to the canister under the coolant reservoir, but if I disconnect this line between the canister and the intake, there is no vacuum on either side. It runs all the way to the throttle body, I assume there should be vacuum at least on that side of it. BTW the original MAP sensor line is now repaired and all other lines checked for breaks. Engine temperature seemed low, replaced the thermostat (could see daylight through it 20 minutes out of the car) and the ECT connector..... now warms up to the halfway point on the gauge, runs pretty well, but the car still occasionally bucks and surges at idle when at low speed even with the TCC disconnected... any ideas?

Also I have disturbed the idle adjustment several times in chasing these problems, it appears to me I should be reading .80 volts return to ECM at idle. Is this correct?

you need to find a shop where they can do a datastream, you need to watch every part when it "skips" it sounds to me like you gat a cam sensor problem also... take your canister off the car turn it over, see if gas comes out of it... I need to know if it does...and plug your tcc back in, flush the trans...<-not just change the filter..
btw dont over analize the problem, its a beretta and a very simple car to repair...

Okay, I think I found the problem... the car has been popping a code 33 for IAC circuit.... I assumed the valve was bad... but I checked the voltages going in. Out of 4 wires going in, 2 have frequent voltage fluctuations anywhere from 2 volts to 13 (with the car running) and the other 2 have a constant .45 volts. I am presuming I should be getting a constant 12-13 volts on at least one circuit. Unplugged the IAC and set the idle adjustment screw up a bit, seems to be fine, just idling up when I take it out of gear, other than the car is running fine now. Could this be a bad ECM?

Okay, I think I found the problem... the car has been popping a code 33 for IAC circuit.... I assumed the valve was bad... but I checked the voltages going in. Out of 4 wires going in, 2 have frequent voltage fluctuations anywhere from 2 volts to 13 (with the car running) and the other 2 have a constant .45 volts. I am presuming I should be getting a constant 12-13 volts on at least one circuit. Unplugged the IAC and set the idle adjustment screw up a bit, seems to be fine, just idling up when I take it out of gear, other than the car is running fine now. Could this be a bad ECM?how high does it idle up?...

how high does it idle up?...

A guesstimate of 1200-1500 rpm, car has no tach. I have had to adjust the idle screw on the throttle body because the engine would not start at a normal adjustment. I do know now that the engine is loading up with fuel. The bucking and surging are occuring with the throttle closed at low speed, and the engine is struggling to stay running because it is running too rich. :screwy:
It has popped a code 44 of lean exhaust from day one, and I am wondering if the 3-year old fuel in the tank may have contaminated the oxygen sensor, making it read lean all the time and forcing the ECM to run too rich? Once the car is stopped, it sputters for a minute or two, and then clears up a bit, which tells me that it still has some exhaust reading. I started it the other night and it sputtered badly and I smelled raw fuel, so I know it is flooding. Once I opened the throttle it cleared right up, but I'm not certain it is causing this problem.

A guesstimate of 1200-1500 rpm, car has no tach. and the engine is struggling to stay running because it is running too rich.
It has popped a code 44 of lean exhaust from day one, the oxygen sensor, making it read lean all the time and forcing the ECM to run too rich? Once the car is stopped, it sputters for a minute or two, and then clears up a bit, which tells me that it still has some exhaust reading. I started it the other night and it sputtered badly and I smelled raw fuel, so I know it is flooding. Once I opened the throttle it cleared right up, but I'm not certain it is causing this problem.sounds like your on the right track with the 02 sensor...

Problem solved..... The ECM was bad..... took long enough to figure it out....

Problem solved..... The ECM was bad..... took long enough to figure it out....I knew it..
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