Does the ecu cause the car to run bad at idle,but once you start going at a good speed it runs o.k.

no car told maker or model or engine size.
there are lots causes that, hard starts
if spark good and strong and even HV spark wire sets fresh.
the short list.

1. bad fuel
2. too much fuel cranked and floods
3. IAC bad, idle air valve stuck and wants to flood cold.
4. cold idle is the big clue, where too low. IAC failing
5. EGR sticking open at idle. possible.
6. if you press gas Pedal, at 5% (about) and starts easy and likes that until it worms up that means the IAC is dead.
7. I stop here lots more, no car told.

all cars modern EFI is it EFI> have IAC and ISC valves 1 or both.
and if stuck idle fails. hot or cold.
no car told why post like that 100 year of cars and 10,000 engines.
????

hi, i would like to advice you check the electronic idle speed control valve and also check engine coolant temp sensor. The ISC (idle speed control valve) is located somewhere below the throttle valve. the engine coolant temp sensor is located near distributor. it has a two wire connection. the sensor connector is usually green

i cant understand that but got BAD idle.
there are different idle speeds, for hot ,warm and cold engine.
and the PCM (ECU) regulates idle with valve called ISC.
bad idle can be 1 of 2 things.
ISC sticking.
or engine runs so bad the ECU can NOT control idle.

clean the ISC, if not that
then its a big job, to find true cause. ASK !
one is finding air leaks.aka, vacuum leaks.

I think you have an engine speed sensor fault. its not reading the engine speed or the motion speed. needs these two to change speed and ( gear). one is connected to the abs unit and the other is on the engine. usually if they both go its down to the gear box ecu. you can check if you have it on a ecu reader. will have fault codes or not be read at all.

rule 1 on all otto cycle gas engines.
idle is the last thing to work right.
on EFI , its under control at all times.
but if the engine runs bad, it goes out of control.
IS THE CHECK ENGINE warn, lamp glowing running, ????
yes, why not get the DTC codes, (flash error codes now)
when it runs bad, is it misfiring, and shaking engine, weak power from engine,, bogging, or only stalling.
low rpm is near stall and is same thing.
1500rpm is perfectly normal for any cold engine.
Hot , its not.
first off check all fuses.
The idle controls are called ISC, "idle speed controller"
its a slave valve and ECU logic and servo controls.
the ECU works overtime , keeping idle right.
if the ISC sticks, it fails.
if the EGR sticks open , the ISC loses control
if the you get intake (induction) air leaks it loses control
same for misfire, gross, flooding. same for gross lean.
so how do we do this? find a cause.\
easy we give that long missed 60,000 mile tune up.
and during that i clean the ISC and EGR main valves.
on any old car like this, wow, its sure to be a mess, if not serviced.

then make sure the EGR main is closed,
engine hot.
i see if my ISC is trying to work.
i then check my fuel mixtures. to see if the engine EFI
reaches and holds closed loop.
oops, it cant be cause the 0xygen sensor died, 100k miles ago.
its dead.
no OTC scan tools for 1995 ( sure hackers have em)
so is very hard to get this information, i use a scope to watch my oxy sensor, if stuck rich i fix that first. if stuck lean , i find the exhaust crank causing it. or other cause... long list of tests.

in a real shop the start at the tail pipe end, OMG this puppy is rich as a pig and work forward, is start at the oxysensor
i get it working by any means.,
then fix idle if not already magically working. as most do (cleaned)

here is a very common example.
1: EGR sticks open at idle. IDLE RPM drops like rock. ( it must)
2: ECU sees illegal RPM and opens the ISC fully, to no avail.
some cars EFI hunts the ISC causing surging.
others ECU just slams the ISC wide open and does a software hope thing. in this case, does nothing,due to gross EGR misfire effects.
the idle controls are a SERVO,. a closed loop servo system.
it regulates idle until , something horrible happens.

it fails when conditions are outside it's range of Authority.

You need to run a fault code test on the ECU. here is how you do that.

I would try replacing the ignition control module and the distributor pickup as the next most likely cause of this problem. Also I would do the following

This problem can be caused by a dirty automatic idle speed control valve and throttle valve. Buy a can of throttle valve cleaner from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

Sometime unplugging sensors is a good way to find a bad one. If the incorrect reading is being supplied to the ecm, sometimes it can't tell.
When a sensor is disconnected, the ecm knows and uses a default value.
Obviously this doesn't work with the crank sensor.

One thing to check is the connector at the coolant resevoir. Sometimes coolant will migrate through the wires and cause all kinds of trouble.

all that an not one RPM stated, making the meter useless.
numbers matter, tell them.
all that can be condensed to idle controls, dead hot.
you took it to a shop but was running great then.
so he guessed, and spent a fortune doing nothing.
why do that. ?
take it in broken, or have them drive it for a day to work.
find a real shop that can do that. and win.,
THE idle controls can fail many a way.
1: the control is bad. (ISC/IAC) they like to stick clean it.
2: vacuum leaks causing above.
3: gross engine misfiring (50 causes)
4: not scanning it. you didnt. so, work blind.

next time post actual RPM, when missing up.
and win, !!!!
the PCM not stuck in LIMP-in mode, will work big time hard
to prevent engines from stalling and to hold spec rpm
700? hot.
the ECU modulates the ISC to hold 700 rpm , HOT, in neutral or DRIVE, if you go P N, D and P, the rpm must hold at spec, 700
if not the ECU is not regulating RPM is it.
and not scanning it now, you may never lean why.
scan cars failing, not working right., and win.

lets say you said, just to show how important numbers are.
RPM is 400 or 500 engine shakes.
EGR stuck open( if it has one,)
or engine gross misfiring ever get a full tuneup this decade, even spark plugs. OMG no>?
injectors leaking or clogged

at the 10min no start.
does 5-10% throttle action (right foot) allow it to start now.
NO, try wide open throttle starts.
bingo, then its flooded
if it floods, post , why does my engine flood. and get other answers
like a tuneup.,

thats it may be the fuel pump, and the reason why its worse when cold its becouse, when you start the engine cold it needs more fuel to function properly and hold a good idle until it gets its normal operating temp, during these moment the ecu increases the injectors pulse duration to get more fuel to the engine and perhaps a low fuel pressure will give bad fuel atomization and it gives you bad idle and cruise quality, I recomend you to check your fuel pressure for abnormal readings it can be easy by the injectors fuel rail, i hope it help's good luck