Cadillac Repair: engine repair or tran, caddliac, rough run

Question
I have an 89 caddliac it starts and runs fine until i put it in drive then it starts to idle rough but when i put it in reverseit will run fine?  

Answer
Hi,George

 Though a few things can cause this,we'll have to do basic checks first,what ive seen with the 87-92 cadillacs is that usually they idle rough in drive is a failing ground ckt{wire},the one that is notorious is the ground cable that goes from the battery to the side of the engine block near the starter motor,there is a stud that is bolted to the engine block and then a lock nut that holds the cable in place,ive seen these come loose and when the engine is running and in gear it causes the cable to loose connection,thus the main ground isnt there for the ecm and modules,causing a rough run condition,check that ground wire and connections at the battery,make sure they are clean and tight,if you need more help contact me and we can look further into it.Thanks

ED