VS 97 strange problem - heres a challenge for the smart ones on here!!

[astormsau]

What were the error codes? when the check engine light comes on you can bridge pin 5 and 6 on the diagnostic connector to find the error codes.
Crank angle sensor dying usually results in the car either cutting out when driving or not starting after the car has been run - its usually heat which causes it to play up.

My suggestions; read the engine codes and determine what the issue reported by the computer is, then take appropriate action. From the list of issues and repairs you have made i'd be suggesting oxygen sensors would help the situation but even at their worst, they will cause rough idle but not the shuddering you are talking about.

Get back to us with the engine codes...

 

[astormsau]

another possibility is the IAC - idle air controller, can cause issues with the car running like crap, as well as the TPS .. make sure they are all connected properly and clean....

 

[Brett_jjj]

The oxygen sensors dont even get used by the ECU (open loop) until the engine has warmed up and is up near its operating temperature.Then, the ECU goes into closed loop mode, and the ECU then starts to process the signals sent from the oxygen sensors to adjust the fuel/air mixtures etc.So if the engine plays up when its cold,you can rule out the problem being caused by oxygen sensors.

 

[Immortality]

ecu goes into closed loop mode fairly quickly, that is why they used heated sensors

 

[Brett_jjj]

Ive checked this out on a tech 1 scantool, and even the heated 02 sensors still take a few minutes to switch to closed loop.Plenty of time to see if its running crook or not.Usually oxygen sensors wont effect the running of the engine that much.They mainly effect the fuel usage and economy,maybe a little bit of power,but they usually wont cause a misfire or really bad running..

 

[hako]

If you've never had this engine running properly since you bought it then it sounds like the motor was bad when bought. So what I'd do is a health check on the engine - screw all plugs out and check their appearance - then do a compression test, both dry and wet which should tell you the general condition of the engine. Otherwise, you'll just be replacing item after item and wasting many $$$$. You can buy a compression gauge for under $40 or 2nd hand or borrow one. If compression is good, check all ignition related items using check procedures outlined in the Gregorys manual (buy or borrow from library). Then do the same for the fuel system.

 

[Immortality]

by then selves probably not, but on a older engine that isn't running right and a few other things not a 100% it will compound. speaking from personal experience here.

something else to try is a good old vacuum test. it will quickly show any major problems

also checking the actual fault codes might be a good idea. it might give a clue to where to look next

 

[Immortality]

a dodgy fuel injector can cause similar symptoms too

 

[Brett_jjj]

Agreed,he says its done it since day 1 of putting the engine in.Id bet its either a bad CAS,the DFI module, or a bad wiring connection somewhere.Or lastly, Id try another ECU to see if that makes any difference.1997_equipe, youve replaced a lot of stuff there.It doesnt leave much more that could be wrong...Id be checking the above mentioned things next.

 

[Brett_jjj]

Yep,agreed, could be blocked injectors,especially if someone got/let dust or dirt get into the fuel rail connections while the engine was out. Would this cause the engine light to come on though? (EDIT) I can answer that myself when I think about it,it would, because it would upset the mixtures and readings on the 02 sensors and put them out of whack..